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We’re Tracking the Impeachment Inquiry of President Donald Trump

Last Updated Nov. 7, 2019

An impeachment inquiry is a process in the House of Representatives to determine whether to vote on impeachment and, if so, on what grounds. If the inquiry leads to a vote on impeachment, and if a majority of representatives vote yes, then the president is impeached, which only means that the matter is referred to the Senate for a trial. After that, if two-thirds of senators also vote yes, only then would the president be removed from office, and the vice president would become the president.

What’s happening now

The House has called for the continuation of the impeachment investigation by approving a resolution setting procedures for going forward. The House Permanent Select Committee on Intelligence has begun making transcripts of the depositions public and will make a public report of its findings.

Then the House Committee on the Judiciary may report articles of impeachment, which would be the grounds on which the House could vote to impeach the President. Before a possible vote on impeachment, both committees will hold one or more public hearings, in which the President may participate.

Possible Charges » Chronology » How Impeachment Works »

Chronology

Here’s what happened, starting at the beginning.

Ambassador targeted by Ukraine Lev Parnas, an American citizen and businessman born in Ukraine, and an associate of his made significant illegal campaign contributions in June 2018 to former Rep. Pete Sessions and related political entities as a part of a plan to influence the United States government to replace U.S. Ambassador to Ukraine Marie Yovanovitch, according to charges filed by the Justice Department. The plan was reportedly at the request of Ukraine’s former chief prosecutor Yuriy Lutsenko. Later that year, Parnas hired President Trump’s personal lawyer Rudy Giuliani, and Giuliani met with Lutsenko about the plan, according to deputy assistant Secretary of State George Kent. On Jan. 9, 2019 Giuliani asked the State Department to issue Viktor Shokin, Lutsenko’s predecessor as Ukraine’s chief prosecutor, a visa to travel to the United States so that he could provide information about corruption in the United States, according to Kent, possibly referring to the same plan to oust Yovanovitch.

Parnas was charged with conspiring to violate the ban on foreign donations in federal elections on Oct. 10, 2019. George Kent, a deputy assistant Secretary of State, testified on Oct. 15, 2019 that Lutsenko had planned a May 2018 meeting with President Trump’s personal lawyer, Rudy Giuliani, for an unknown purpose, but that the meeting never ocurred, and that they later met in early 2019, and that Giuliani asked the State Department to issue a visa to Shokin.

Political research Around May 2019, President Trump’s personal lawyer Rudy Giuliani was working on behalf of the President and in collaboration with Parnas, the businessman, to persuade the State Department and Ukrainian officials to investigate actions by former Vice President Joe Biden, the President’s chief 2020 election rival at the time, and his son. Trump and his associates accuse Biden of using his position as vice president, around 2016, to help a Ukrainian energy company which made payments to his son by ousting Shokin, Ukraine’s chief prosecutor at the time, who, they claim, was investigating the company, although the accusation of corrupt intent and the claim that Shoken was investigating the energy company are both unsubstantiated. Giuliani told Fox News on Oct. 2, 2019, “I explored [the accusation] as part of my duty as an attorney to show that the crimes committed, were not by my client, but by Democrats.”

Lutsenko, the Ukrainian chief prosecutor who succeeded the ousted Shokin, said there was no evidence Biden or his son committed a crime. George Kent, a deputy assistant Secretary of State, testified on Oct. 15, 2019 that the State Department considered both Shokin and Lutsenko to be corrupt prosecutors.

Ambassador fired Then on May 20, 2019, the U.S. Ambassador to Ukraine Marie Yovanovitch was fired allegedly for not pushing Ukraine to investigate Biden.

This was first reported on Oct. 3, 2019.

Military aid funding halted On July 18, 2019, President Trump ordered a hold on military aid funding to Ukraine because he wanted European countries to do more to support Ukraine and to pressure Ukraine to address broad corruption issues, according to Trump and the White House.

This was first reported on Aug. 28, 2019.

Key documents

Transcript of Amb. Yovanovitch’s Oct. 11, 2019 deposition by the House Intelligence Committee [released Nov. 4, 2019]

The first “quid pro quo” Ambassador Gordon Sondland, who is ambassador to the European Union (of which Ukraine is not a part), told Ukraine on July 10, 2019 that an investigation into Biden was a precondition for a coveted White House visit by Ukraine’s president. Then on July 25, 2019 (before the Trump-Zelenskyy call), volunteer special envoy to Ukraine Kurt Volker told Ukraine President Zelenskyy’s top adviser, in a text message, “assuming President Z convinces Trump he will investigate . . . we will nail down date for visit to Washington.”

Alexander Vindman, a White House adviser, and Bill Taylor, the top diplomat in Ukraine, testified that an announcement of an investigation into the energy company tied to Biden’s son was a precondition for the White House visit. Vindman testified about Sondland’s communication to Ukraine. Sondland testified later that they intended to (but ultimately did not) ask Ukraine to announce that the investigation would be opened, denied that it was in exchange for the White House visit, but nevertheless felt, in retrospect, that the request alone would have been “improper” because of its relevance to the upcoming 2020 election. Volker provided the text messages to the House Foreign Affairs Committee on Oct. 3, 2019. Vindman’s testimony was on Oct. 29, 2019. Sondland testified on Oct. 17, 2019.

Key documents

Text messages between July 19 and Sept. 9, 2019 between ambassadors Volker, Taylor, Sondland

Alexander Vindman’s Opening Statement (Oct. 29, 2019)

Summary of the Trump-Zelenskyy call [released Sept. 25, 2019]

Gordon Sondland’s Testimony (Oct. 17, 2019)

Bill Taylor’s Testimony (Oct. 22, 2019) [released Nov. 6, 2019]

Trump-Zelenskyy call In a July 25, 2019 call between President Trump and Ukraine’s new President Zelenskyy, Trump urged Zelenskyy to investigate alleged actions by Biden (“Biden went around bragging that he stopped the prosecution [into the Ukrainian energy company] so if you can look into it...,” Trump said on the call) and to locate the Democratic National Committee (DNC)’s 2016 email server (“The server, they say Ukraine has it,” Trump said), which was hacked by Russia in an effort to help the President win the 2016 election, and to do both investigations in collaboration with Giuliani, the President’s personal lawyer. Zelenskyy replies that they will “look into the situation” related to the Ukrainian energy company that Biden is accused of helping. Several weeks later, Zelenskyy learned that the military aid had been put on hold, but not why. Text messages between the ambassadors following the call show a debate between the ambassadors over whether Trump was withholding aid to Ukraine and an invitation to visit the White House in exchange for an investigation into Biden, or whether it was in the furtherance of legitimate foreign policy goals such as encouraging Ukraine to resume its own anti-corruption efforts.

On Sept. 25, 2019 the White House released a summary of the Trump-Zelenskyy call. Ambassador Kurt Volker provided the text messages to the House Foreign Affairs Committee on Oct. 3, 2019.

Whistleblower complaint A government employee whose identity has been withheld filed a confidential whistleblower complaint on Aug. 12, 2019, documenting the Trump-Zelenskyy phone call, efforts to restrict access to records related to the call, and the events leading up to the call. In the following weeks, Trump-appointed officials disagreed about whether to share the complaint with Congress and ultimately withheld it and stored the call’s rough transcript (the call summary) in a classified computer system.

The existence of the complaint was not known until Sept. 21, 2019, when key elements of the complaint were leaked to the media. The White House made the complaint available on Sept. 26, 2019.

Key documents

Whistleblower complaint [released Sept. 26, 2019]

The second “quid pro quo” On Sept. 1, 2019, Ambassador Sondland told Ukraine that military aid would be withheld unless it made a public statement that it would investigate the energy company that made payments to Biden’s son and “2016,” referring to the 2016 hack of the DNC’s email server, following a directive given by President Trump via his personal lawyer, Giuliani. Zelenskyy planned to make the statement on CNN on Sept. 13, 2019, but the withheld military aid was restored on Sept. 11, 2019, possibly as a result of pressure from legislators in Congress who believed the White House was wavering in its support for Ukraine against Russia. Nevertheless, on Oct. 4, 2019, Ukraine said it would open the investigation.

Ambassador Bill Taylor, the top diplomat in Ukraine, and Tim Morrison, a White House advisor, testified that the aid was in exchange for Ukraine investigating the energy company, on Oct. 22, 2019 and Oct. 31, 2019, respectively. Gordon Sondland initially denied that an investigation was contingent on military aid in his Oct. 17, 2019 testimony, saying the President told him “There is no quid pro quo.” But on Nov. 5, 2019, Sondland revised his testimony, saying that military aid had indeed been contingent on announcing an investigation into the energy company that made payments to Biden’s son and “2016,” referring to the 2016 hack of the DNC’s email server..

Key documents

Bill Taylor’s Opening Statement and Testimony Transcript (Oct. 22, 2019) [transcript released Nov. 6, 2019]

Tim Morrison’s Opening Statement (Oct. 31, 2019)

Gordon Sondland’s Oct. 17, 2019 Testimony & Nov. 5, 2019 Revised Statement [released Nov. 5, 2019]

Impeachment inquiry On Sept. 21, 2019, key elements of the whistleblower complaint were leaked to the media. On Sept. 24, 2019, Speaker of the House Nancy Pelosi announced an inquiry into the impeachment of President Trump, saying that "the President has admitted to asking the President of Ukraine to take actions which would benefit him politically." 

Release of documents The next day on Sept. 25, 2019 the White House released a summary of the Trump-Zelenskyy call. And after the Senate and House voted unanimously on Sept. 24-25 on non-binding resolutions demanding access to the whistleblower complaint, and minutes before the Director of National Intelligence’s Sept. 26, 2019 appearance before the House Intelligence Committee, the White House made the complaint available to Congress, which then made it available to the public.

On Sept. 25, 2019 the White House released a summary of the Trump-Zelenskyy call and on Sept. 26, 2019 the White House provided the whistleblower complaint.

Key documents

Senate resolution (Sept. 24, 2019) and House vote (Sept. 25, 2019) on resolution demanding the whistleblower complaint

House vote demanding whistleblower complaint
House vote demanding whistleblower complaint

Text messages released On Oct. 3, 2019, special envoy Kurt Volker, who had participated in the text messages, was interviewed by the House Foreign Affairs Committee in a closed session. Volker provided the text messages between U.S. ambassadors, which were then made public by the House Foreign Affairs Committee. Democrats and Republicans have given otherwise inconsistent accounts of the substance of the interview. Additionally, the reason why Ambassador Marie Yovanovitch was fired earlier in the year was first reported. And, President Trump asked Ukraine to investigate Biden in a press conference on the White House lawn.

President Trump asks Ukraine to investigate [video]

Obstruction The House Committee on Oversight subpoenaed a slew of documents from White House staff, including Chief of Staff Mick Mulvaney and Secretary of State Mike Pompeo, and requested documents from Vice President Mike Pence without a subpoena. In response, the White House sent a letter to the House on Oct. 8, 2019 stating that it will not cooperate with the subpoenas or the impeachment inquiry because, they say, the House is not affording the President due process rights as he would have in a criminal trial — but the Constitution is clear that an impeachment is not a criminal trial. Refusal to cooperate with subpoenas could likely become another impeachment charge, as it was in the case of President Richard Nixon.

Public investigation On Oct. 31, 2019, the House passed an impeachment resolution making the impeachment investigation official and outlining its next stages. It requires at least one open hearing in which Democrats and Republicans are given equal time to question witnesses and allows deposition transcripts to be published at the discretion of the House Intelligence Committee. Republicans previously protested a lack of transparency in the impeachment investigation, but no Republicans voted for the resolution.

Depositions During October 2019, congressional committees conducted thirteen private interviews and briefings with Trump Administration officials. Marie Yovanovitch, the fired ambassador to Ukraine, said in her opening statement obtained by the Associated Press that she was ousted “based, as best as I can tell, on unfounded and false claims by people with clearly questionable motives.” Ambassador Taylor said in his opening statement on Oct. 22, 2019 that Volker, Sondland, Secretary Rick Perry, Sen. Ron Johnson, and Giuliani began an “irregular” circumvention of normal State Department relations with Ukraine to push investigations related to Biden and the 2016 hack of the DNC email server. Private interviews are a standard procedure for committee investigations, especially when national security interests are involved, and the full House most recently re-authorized their use on Jan. 9, 2019. Both parties participate in the interviews.

Depositions

Kurt Volker
Volunteer Special Envoy to Ukraine
Oct. 3, 2019 — Says Ukraine did not know why aid was withheld. Also provided text messages. Opening Statement. Transcript.
Fiona Hill
White House Adviser
Oct. 14, 2019 — Says Gordon Sondland, ambassador to the European Union and not Ukraine, was circumventing normal relations with Ukraine with the White House.
George Kent
Deputy Assistant Secretary of State
Michael McKinley
Adviser to Secretary of State Mike Pompeo
Gordon Sondland
Ambassador to the European Union
Oct. 17, 2019 — Says he initially thought U.S. was pressuring Ukraine on legitimate anti-corruption issues and that military aid was not being withheld for any reason, but later learned that President Trump wanted Ukraine to investigate “He wanted [the Ukrainian energy company] and 2015 election mentioned.” (“I do not recall any discussions with the White House on withholding U.S. security assistance from Ukraine in return for assistance with the President's 2020 re-election campaign.” “The President responded, ‘Nothing. There is no quid pro quo.’ ”) However, on Nov. 5, 2019, Sondland submitted a new statement saying that military aid was in exchange for an investigation by Ukraine into the energy company Biden is accused of helping. Opening Statement. Transcript and Revised Statement (Nov. 5, 2019).
Bill Taylor
Top Diplomat in Ukraine
Oct. 22, 2019 — Says Volker, Sondland, and others began an “irregular” circumvention of normal State Department relations. Opening Statement. Transcript.
Laura Cooper
Deputy Assistant Secretary of Defense
Oct. 23, 2019 — The substance of her testimony has not been publicly reported.
Philip Reeker
State Department Official
Oct. 26, 2019 — The substance of his testimony has not been publicly reported.
Alexander Vindman
White House Adviser
Oct. 29, 2019 — Says Sondland told Ukraine on July 10, 2019 that an investigation into Joe Biden was a precondition for a White House visit. Opening Statement.
Catherine Croft
State Department Official
Timothy Morrison
White House Advisor
Oct. 31, 2019 — Says “I was not concerned that anything illegal was discussed” on the Trump-Zelenskyy call. Opening Statement.

Previous impeachment votes This is not the first time impeachment of President Trump was proposed — in fact, the House of Representatives has already voted on impeachment three times, rejecting impeachment each time. In December 2017 the House voted 58 to 364 and in January 2018 the House voted 66 to 355 against impeachment based on Trump’s equivocating comments after the white supremacy march in Charlottesville, Virginia and his calls as a presidential candidate to ban all Muslim immigration. In July 2019, the House voted 95 to 332 against impeachment based on Trump’s racist tweet that four congresswomen should “go back” to where they came from. [See how representatives’ votes changed.]

July 2019 House vote on impeachment
Vote to kill earlier 2019 impeachment resolution

Possible Impeachment Charges

The Constitution gives the House of Representatives the power to impeach — or charge — a president and other government officials for “treason, bribery, or other high crimes and misdemeanors.” (If the House votes to impeach, the charges go to the Senate for a trial to determine if the official should be removed from office. See How Impeachment Works.) Below we list some of the charges that the House of Representatives may consider.

What is impeachable?

Although treason is defined in the Constitution and bribery is defined by a criminal statute, “high crimes and misdemeanors” was left open to interpretation. Based on historical statements by framers of the Constitution and subsequent practice by Congress, impeachment is not limited to criminal acts. Courts have also determined that Congress’s choice to impeach and remove an official is not subject to review by courts. Therefore, Congress may remove a president or official for any reason or no reason at all.

Instead of looking at what’s legal (since any basis for impeachment and removal is legal), one can also look at what’s normal. President Andrew Johnson was impeached in 1867 over his firing of his Secretary of War — the House of Representatives viewed the action as a violation of the Tenure of Office Act, while Johnson considered the Act unconstitutional. The Senate found Johnson not guilty. (Interestingly, the Tenure of Office Act was later repealed, and the Supreme Court took Johnson’s position in a similar case in the next century.) The House of Representatives impeached President Bill Clinton in 1998 for lying to a grand jury and obstruction of justice related to a matter unrelated to his official duties and for which there was no underlying crime. The Senate found Clinton not guilty. In 1974, the House Judiciary Committee recommended that President Richard Nixon be impeached for obstructing an investigation into criminal activities by his administration and re-election campaign, abuse of power, and not complying with subpoenas. Nixon resigned before the full House took any action.

For more information, see What Are “High Crimes and Misdemeanors”? (Slate) and Impeachment and Removal (CRS).

What charges are being considered for President Trump?

Foreign Assistance in the Election The White House has said that in a July 25, 2019 phone call, President Trump asked Ukraine president Volodymr Zelenskyy for a “favor” to investigate the President’s chief political opponent at the time, former vice president Joe Biden (“Biden went around bragging that he stopped the prosecution [into the Ukrainian energy company that paid his son] so if you can look into it...,” Trump said on the call) and to locate the Democratic National Committee (DNC)’s 2016 email server (“The server, they say Ukraine has it,” Trump said on the call). The President asked Zelenskyy to coordinate the investigations with the President’s personal lawyer, Rudy Giuliani, who told Fox News on Oct. 2, 2019, “I explored [the accusation] as part of my duty as an attorney to show that the crimes committed, were not by my client, but by Democrats.” Trump and his associates accuse Biden of using his position as vice president, around 2016, to help a Ukrainian energy company which made payments to his son, although the accusation is unsubstantiated. Although the President has said he asked Zelenskyy for a legitimate investigation into corrupt acts by Biden, whether or not Biden acted improperly is not actually at issue. The President’s motivation is the central component of this potential charge. The President’s focus on domestic issues related to the 2016 presidential election (in which he won) and a likely candidate in the 2020 presidential election (who he will likely run against), and not any other corruption in Ukraine, and the involvement of the President’s personal lawyer who said he is being paid to pursue partisan goals, suggest the President’s motivation may have been political. Foreign entities are prohibited by law from making contributions to political campaigns, including by providing favors of material value, and an impeachment charge could be based on a violation of law or perceived norms for foreign interference in elections or abuse of power.

Quid Pro Quo One of the President’s foreign policy goals has been to get European countries to step up their support for military security, rather than relying on the United States. According to the White House, in the July 25, 2019 Trump-Zelenskyy phone call, the President told Zelenskyy that he thought the United States’s security aid to Ukraine made the nations’ relationship not “reciprocal,” and then in his next sentence asked Zelenskyy for the “favor” described above. Trump told Zelenskyy, “it’s very important that you do it.” Additionally, prior to the call, on July 10, 2019, Ambassador Gordon Sondland told a high-ranking Ukrainian official that a previously extended invitation for Zelenzyy to meet President Trump at the White House was on the condition that Ukraine investigate Joe Biden, according to testimony by White House adviser Alexandar Vindman. On the Trump-Zelenskyy call, Zelenskyy replies that they will “look into the situation” related to the Ukrainian energy company that Biden is accused of helping. Although not stated in clear words on the call, Zelenskyy may have understood the President as asking Ukraine to make the relationship reciprocal by performing the favor in exchange for either the military aid that Ukraine already receives from the United States or for a meeting with Trump at the White House — a quid pro quo. Quid pro quo is a generally accepted tool in foreign policy and well within the President’s foreign policy powers — so long as the President is conducting foreign affairs. If an investigation into Biden is deemed to be a political or domestic matter, and not a legitimate foreign policy goal, an impeachment charge might be based on violating bribery law, abuse of power, or the norms around the President not interfering in domestic law enforcement cases.

Extortion On July 18, 2019, the President had halted military security aid to Ukraine, and the President’s ambassador to the European Union told Zelenskyy in September 2019 that the military aid was withheld until Ukraine announced an investigation into the energy company tied to Joe Biden’s son, according to Ambassador Bill Taylor in his deposition and Tim Morrison, a White House advisor, in his deposition. Withholding aid and a White House visit to coerce Ukraine to perform an investigation is extortion, but extortion is a generally accepted tool in foreign policy and well within the President’s foreign policy powers — so long as the President is conducting foreign affairs. If an investigation into Biden is deemed to be a political or domestic matter, and not a legitimate foreign policy goal, an impeachment charge might be based on extortion, which is a crime.

Emoluments According to the White House, in the July 25, 2019 phone call between President Trump and Ukraine president Volodymr Zelenskyy, Zelenskyy said he had stayed at the President’s Trump Tower property on his last visit to the United States, among other thanks and praise, to which the President responded positively. Since the President personally benefits from business at his properties, foreign leaders’ stays at his properties may be a constitutionally prohibited emolument.

Coverup – Mishandling Records A verbatim transcript of the July 25, 2019 Trump-Zelenskyy phone call was filed in a location meant for classified materials, the White House confirmed, even though the call did not involve classified information, according to the whistleblower complaint, in order to restrict access to it. It was also reported that a transcript of a call with China was placed in the same system. Several laws including the Presidential Records Act require presidential records like the verbatim transcript to be preserved but may not require that the records be stored in any particular electronic system. (What has often been described as the public transcript of the call is actually a summary of the call produced by the White House — it is not known whether the White House accurately summarized the verbatim transcript.)

Coverup – Withholding Whistleblower Report Although the whistleblower report was written on Aug. 12, 2019 and was deemed by a Trump-appointed nonpartisan civil servant to be credible, it was withheld from Congress by a Trump-appointed political appointee, the Director of National Intelligence, possibly in violation of existing law that requires that credible complaints be forwarded confidentially to Congress.

Obstruction The White House sent a letter to the House committees conducting the impeachment inquiry stating that it will not respond to the committees’ subpoenas because, they say, the House is not affording the President due process rights as he would have in a criminal trial — but an impeachment is not a trial. If the House completes the inquriy and votes to impeach, which is similar to preparing a list of charges, then only at that point would a trial will be held in the Senate. Refusal to cooperate with subpoenas could likely become another impeachment charge, as it was in the case of President Richard Nixon. Failure to comply with a congressional subpoena is a crime.

How Impeachment & Removal Works

Impeachment is the first step in the Constitutional process for Congress to remove the president or other government officers. Although the Constitution sets a broad two-step process for impeachment and removal, there are many steps that have evolved from previous times impeachment and removal have been used on lower government officers, such as judges. No president has ever been removed from office.

Below you’ll find a simplified timeline of how impeachment and removal works, and some links to research reports that provide more detailed information.

A Simple Timeline for Impeachment and Removal

Impeachment in the House of Representatives

① Impeachment Inquiry On Sept. 24, 2019, Speaker of the House Nancy Pelosi announced that the House of Representatives will move forward with an official impeachment inquiry. This announcement alone is enough to begin official impeachment proceedings, starting with the directive that six House committees continue their investigations of the President “under that umbrella of impeachment inquiry.”

② Investigative Authority In the cases of Presidents Nixon and Clinton, a resolution was necessary to grant the House Judiciary Committee with authorities to conduct an investigation into impeachment. However, under the current House rules, the committee already has those authorities. ← We are here.

③ Committee Reports After investigating, committees will report their findings to the House as a whole. In the past, the House Judiciary Committee has voted on whether to recommend impeachment and has reported an impeachment resolution with specific allegations of misconduct. Each investigating committee may report separate findings.

④ Vote on Impeachment The House would then vote on an impeachment resolution containing articles of impeachment, which are the charges of misconduct. This vote only requires a simple majority for passage. If passed, the subject of the inquiry is impeached — which means the matter is referred next to the Senate.

Trial in the Senate

⑤ Preparation for a Trial If the House chooses to impeach, there will be a trial in the Senate to determine if the President is guilty. To start this process, the House will select “managers” to present evidence to the Senate and to subpoena witnesses, and the Senate will issue a writ of summons to the impeached official to appear.

⑥ Trial The trial is roughly analogous to a criminal court trial, with the House managers playing the role of the prosecution, the Senate as the jury, the Chief Justice of the Supreme Court as the judge, and the impeached official is the defendant. However, the Constitution is clear that it is not a criminal trial, since the standards for evidence and conviction are up to the Senate.

⑦ Deliberation Similar to a jury, the Senate meets in closed session to deliberate the substance of the trial.

⑧ Vote on Conviction Finally, the Senate votes on each article of impeachment separately. These votes require a ⅔rd majority to convict, which results in removal from office. The Senate may also vote on whether the convicted official becomes disqualified from holding a government position again, for which only a simple majority is required.

Appealing a Conviction

⑨ Judicial Review Impeachment proceedings have been challenged in federal court on a number of occasions. In the unlikely event that the president is impeached and the Senate convicts him, there may be lawsuits to appeal the conviction. However, courts have said in the past that Congress’s power to impeach is broad and in many cases is not subject to judicial review.

Research Reports

These research reports provide additional information about the impeachment process.

Impeachment and Removal (Congressional Research Service; Oct. 29, 2015)

The Impeachment Process in the House of Representatives (Congressional Research Service; Aug. 12, 2019)

Congressional Resolutions on Presidential Impeachment: A Historical Overview (Congressional Research Service; Sept. 16, 1998)

Constitution Annotated: Art II., Sec. 4, Impeachment (Congressional Research Service)