What is impeachment and how does it work? 10 facts to know.

Must the Senate hold a trial? How does Trump differ from Clinton? Can the president pardon himself? And much more.

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By Pete Williams, Alex Moe and Frank Thorp V

WASHINGTON — The congressional power to remove a president from office through impeachment is the ultimate check on the chief executive. No president has ever been forced from the White House that way, although Richard Nixon resigned rather than having to face the near certainty that he would be removed from office.

Congress derives the authority from the Constitution. The term "impeachment" is commonly used to mean removing someone from office, but it actually refers only to the filing of formal charges. If the House impeaches, the Senate then holds a trial on those charges to decide whether the officer — a president or any other federal official — should be removed and barred from holding federal office in the future.

The House has impeached 19 people, mostly federal judges. Two presidents, Andrew Johnson and Bill Clinton, were impeached, but the Senate voted not to convict either of them. Nixon resigned after the Judiciary Committee approved three articles of impeachment but before the full House voted on them.

President Clinton walks to the podium to deliver a short statement on the impeachment inquiry in the Rose Garden of the White House on Dec. 11, 1998.J. Scott Applewhite / AP file

The Constitution provides that a president can be impeached for "treason, bribery, or other high crimes and misdemeanors." Treason and bribery are well understood, but the Constitution does not define "high crimes and misdemeanors."

Congress has identified three types of conduct that constitute grounds for impeachment, including misusing an office for financial gain. But the misdeeds need not be crimes. A president can be impeached for abusing the powers of the office or for acting in a manner considered incompatible with the office.

When Gerald Ford was a member of the House, he defined an impeachable offense as "whatever a majority of the House of Representatives considers it to be at a given moment in history." In other words, impeachment and conviction by Congress is a political punishment, not a criminal one.

1. What constitutes an impeachable offense?

The founders intentionally kept the term "high crimes and misdemeanors" vague, because impeachment is meant to be a political act, not a legal one. Unlike in criminal law, there are no clear rules for evaluating when a president has stepped over the constitutional line.

The founders rejected the term "maladministration" as grounds for impeachment. They didn't want a president tossed out simply because Congress didn't think he was doing a good job. Alexander Hamilton said impeachable offenses were those that involved abuse of public trust. The term is generally understood to mean abuse of office that results in harm to the public.

The House impeached Andrew Johnson in 1868 during a fight over reconstruction after the Civil War. Most of the articles of impeachment accused him of violating a federal law, since repealed, that said a president could not remove certain officials without Senate approval.

President Richard Nixon announces that he will not allow his legal counsel, John Dean, to testify on Capitol Hill on the Watergate investigation in 1973.Charlie Tasnadi / AP file

The House Judiciary Committee approved three articles of impeachment against Nixon in 1974, charging him with:

  • Obstruction of justice, for impeding the investigation into the break-in at Democratic National Committee headquarters in the Watergate office building;
  • Abuse of power, for trying to use the CIA, FBI and other agencies to cover up the Watergate conspiracy; and
  • Contempt of Congress, for refusing to turn over material in response to congressional subpoenas.

The House approved two articles of impeachment against President Bill Clinton in 1998, charging him with:

  • Lying under oath to a grand jury about the nature of his relationships with Monica Lewinsky and Paula Jones; and
  • Obstruction of justice, for encouraging Lewinsky and others to make false statements and concealing gifts he had given her.

2. How is the Trump investigation different from what happened with Clinton?

Three committees in the House — Intelligence, Oversight and Foreign Affairs — are conducting investigations, gathering documents and calling witnesses in the inquiry into Trump. In the Clinton impeachment, one committee, the House Judiciary, relied heavily on a report compiled by Kenneth Starr, the independent counsel who led the investigation, that listed 11 possible grounds for impeachment in four categories — perjury, obstruction of justice, witness tampering and abuse of power.

House Speaker Nancy Pelosi, D-Calif., has said that while the Intelligence Committee will take the lead in investigating Trump, the actual vote on specific articles of impeachment will be conducted by the Judiciary Committee and could draw on the conclusions of other House committees, too, though that seems unlikely. The process of voting on the articles, known as the committee mark-up, will be televised and will likely take place over several days.

House Judiciary took six days to recommend articles of impeachment against Nixon in July 1974 and three days to recommend articles of impeachment against Clinton in December 1998.

If approved by a simple majority, the articles are reported to the full House and are privileged, meaning they can come up for immediate consideration, including potentially several days of debate. The president is impeached if the House approves any of the articles of impeachment by a simple majority vote. The House then appoints members to serve as "managers," or prosecutors, for the Senate trial.

3. Must the House pass a resolution to officially launch an impeachment investigation?

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The Constitution imposes no such requirement, and House rules don't either, even though authorizing resolutions were passed in each of the three previous presidential impeachments.

Rep. Peter Rodino, D-N.J., who was chairman of House Judiciary in 1974 during the Nixon case, called passing a resolution "a necessary step." House rules does not place jurisdiction over impeachment in any specific committee, and Rodino said that in past impeachments the House had passed a resolution to give the investigating committee subpoena power. But the current House leadership has said that such a resolution isn't needed, because the relevant committees already have the necessary subpoena and staffing authority.

Chairman of the House Judiciary Committee Peter Rodino reads his opening statement during an impeachment hearing against President Richard Nixon on May 9, 1974.Bettmann Archive via Getty Images

White House counsel Pat Cipollone is correct in saying that the House "has never attempted to launch an impeachment inquiry against the president without a majority of the House taking political accountability for that decision" by passing a resolution.

But such a vote is not required. The House has voted to impeach federal judges without passing a resolution to authorize an investigation, and the House procedure for impeaching judges and presidents is the same. Even so, House Democrats will hold a vote Thursday to clarify the rules for public hearings, even though a federal judge said on Oct. 25 that "a House resolution has never, in fact, been required to begin an impeachment inquiry."

4. Would passing a resolution give Congress authority to get grand jury material, such as evidence gathered during the Robert Mueller investigation?

Not necessarily. A fight over this issue is now in federal court, and the House won the first round.

The House leans on what happened in 1974. After a federal grand jury in Washington finished an investigation of the Watergate scandal, it prepared a special report on its findings and recommended that its work be forwarded to the House Judiciary Committee, which had begun impeachment proceedings.

Judge John Sirica ruled that while the grand jury's work was secret, he had the authority to release the material to the House. He said that the normal reasons for keeping grand jury proceedings secret — such as preventing the escape of someone who might be indicted or insulating the grand jury from outside influence — no longer applied once the grand jury's work was done. And he noted that Nixon did not object to letting the House committee get the material. That's an important fact.

A federal appeals court agreed with Sirica's decision, and the grand jury material was turned over to the House.

Since then, the federal courts have narrowed the power of judges to declare exceptions to grand jury secrecy. Earlier this year, for example, the D.C. Circuit Court of Appeals said in a different case that there's no exception allowing historians to get access. The court said it interpreted what Sirica did in Watergate as allowed under a federal rule that allows giving grand jury material to the House for "judicial proceedings." But that was said in a footnote: It was not the holding in the case, and that comment did not make any new law.

The Justice Department's view is that the issue isn't settled. It said in a recent filing in the current lawsuit that no court has ever squarely decided whether a House impeachment proceeding qualifies as an exception to longstanding rules of grand jury secrecy. And if Trump — unlike Nixon — explicitly objects to turning the material over, that could be a decisive factor.

In late October, Federal District Court Judge Beryl Howell ordered the Justice Department to give the House Judiciary Committee an unredacted version of the Mueller report, along with some underlying materials. She concluded that the requirement for preserving grand jury secrecy was outweighed by the House Judiciary Committee’s need for the material in its impeachment investigation. The Justice Department immediately appealed.

5. Do the president’s lawyers get to participate in the House impeachment hearings?

This point is sometimes misunderstood. After the White House counsel complained that no Trump lawyers have been allowed to take part in the House committee sessions, many commentators said that the criticism was misplaced, because Trump's lawyers would get their chance in the Senate trial, not in the House proceeding. But that's not how it has worked before.

White House Counsels Bruce Lindsey, left, and Charles Ruff depart the White House with President Bill Clinton's personal attorneys Nicole Seligman and David Kendall, right, on Feb. 12, 1999.Khue Bui / AP file

In both the Nixon and Clinton proceedings, lawyers for the president were involved in the House impeachment process. In 1974, the Judiciary Committee gave Nixon's lawyers copies of documents and evidence, allowed them to sit in on all hearings, including those in executive session, and permitted them to question witnesses who testified before the committee. Clinton's lawyers were likewise allowed to present witnesses and to briefly question Starr, the independent counsel whose report formed the backbone of the case for impeachment.

In the current proceedings, the House Judiciary Committee recently adopted a rule allowing the president's lawyers to respond to evidence and testimony in writing. But there is no requirement for such an accommodation to the president's lawyers, and there was no such arrangement when the House impeached Andrew Johnson.

6. Must the Senate hold a trial, or can it simply sit on the House articles of impeachment?

The Constitution simply says the Senate has "the sole power to try all impeachments," and some scholars have suggested this means the Senate is empowered but not required to carry out this function. But Senate rules suggest that it's a duty, not an option. Note the word "shall" in Senate Impeachment Rule One:

"Whensoever the Senate shall receive notice from the House of Representatives that managers are appointed on their part to conduct an impeachment against any person and are directed to carry articles of impeachment to the Senate, the Secretary of the Senate shall immediately inform the House of Representatives that the Senate is ready to receive the managers for the purpose of exhibiting such articles of impeachment, agreeably to such notice."

In any event, Senate Majority Leader Mitch McConnell, R-Ky., has said: "Under the impeachment rules of the Senate, we'll take the matter up. ... We intend to do our constitutional responsibility."

7. How does a Senate trial work?

The Constitution lays out only three requirements: The chief justice presides over the Senate trial of a president (but not the trial of any other official); each senator must be sworn (similar to the way jurors take an oath); and a two-thirds vote is required to convict on any article of impeachment.

Once the preliminaries are out of the way, the trial takes place under procedures similar to courtrooms. The House managers make an opening statement, followed by a statement from lawyers for the president.

During impeachments of judges, the evidence is generally presented during committee hearings at which the House managers call their witnesses, who can be cross-examined. And then the reverse happens, with the president's counsel calling witnesses who can be cross-examined by the House managers. The Senate has yet to decide whether, if Trump is impeached, witnesses will be allowed to testify to the full Senate.

Reporters listen to Monica Lewinsky's testimony during the Senate impeachment trial of President Bill Clinton in 1999.David Hume Kennerly / Getty Images file

There's no requirement for the president to appear, and he cannot be compelled to testify.

Like jurors in a trial, senators sit and listen. The rules say if they have questions, they can submit them in writing to be asked by the chief justice.

After both sides make their closing arguments, the Senate begins deliberations, traditionally in closed session. The Senate then votes separately on each article of impeachment, which must take place in open session.

8. What is the role of the chief justice?

It's limited. The Senate has not adopted rules of evidence, but the rules give the chief justice the authority to decide on all evidentiary questions. He can also put the questions to the full Senate for a vote on admissibility. Chief Justice William Rehnquist, who presided over the Clinton impeachment, quoted from Gilbert and Sullivan in responding to a letter inquiring about his time as presiding officer: "I did nothing in particular, and I did it very well."

9. Could the president pardon himself if he's impeached?

No. The same constitutional provision that gives the president the power "to grant reprieves and pardons for offenses against the United States" adds this phrase: "except in cases of impeachment."

10. What would happen if the Senate convicted Trump?

He would be immediately removed from office, triggering the 25th Amendment. Vice President Mike Pence would become president.

U.S. President Donald Trump speaks to reporters as he arrives for a meeting at the Pentagon, accompanied by Vice President Mike Pence in Arlington, Virginia on Jan. 18, 2018.Carlos Barria / Reuters

That would create a vacancy in the office of vice president, so Pence would nominate someone to succeed him, who would become vice president upon confirmation by both houses of Congress.

This is the procedure followed when Nixon resigned. Ford, the vice president, became president and nominated as vice president former New York Gov. Nelson Rockefeller, who was confirmed after extensive congressional hearings.