The account from the former F.B.I. director James B. Comey of President Trump pressing him to drop an investigation into Michael T. Flynn, the former national security adviser, has escalated talk among the president’s critics that his actions may amount to obstruction for justice and grounds for impeachment.
前联邦调查局（FBI）局长詹姆斯·B·科米（James B. Comey）称，特朗普总统曾向其施压，要求停止调查前国家安全顾问迈克尔·T·弗林（Lt. Gen. Michael T. Flynn），此事进一步加剧总统批评者的不满，他们认为他的行动或许构成了妨碍司法公正，并成为弹劾的依据。
“Asking F.B.I. to drop an investigation is obstruction of justice,” Representative Ted Deutch, Democrat of Florida, wrote on Twitter on Tuesday. “Obstruction of justice is an impeachable offense.”
But several legal specialists across party lines cautioned that talk of impeachment is premature while the facts remain unclear; the White House has denied that Mr. Trump pressured Mr. Comey to drop the case.
Still, the early chatter has heightened interest in how the impeachment process works. Here’s what you need to know:
What is impeachment?
The Constitution permits Congress to remove presidents before their term is up if enough lawmakers vote to say that they committed “treason, bribery, or other high crimes and misdemeanors.”
Only three presidents have been subjected to impeachment proceedings. Two were impeached but acquitted and stayed in office: Andrew Johnson in 1868 and Bill Clinton in 1998 and 1999. A third, Richard M. Nixon in 1974, resigned to avoid being impeached.
只有三位总统面临过弹劾程序。其中两位虽遭到弹劾，但被宣告无罪并得以留任：1868年的安德鲁·约翰逊（Andrew Johnson），以及1998和1999年的比尔·克林顿（Bill Clinton）。第三位是1974年的理查德·M·尼克松（Richard M. Nixon），他为免遭弹劾而辞职。
What is the process?
First, the House of Representatives votes on one or more articles of impeachment. If at least one gets a majority vote, the president is impeached — which essentially means being indicted. （In both the Nixon and the Clinton cases, the House Judiciary Committee considered the matter first.）
Next, the proceedings move to the Senate, which holds a trial overseen by the chief justice of the Supreme Court. A team of lawmakers from the House, known as managers, play the role of prosecutors. The president has defense lawyers, and the Senate serves as the jury.
If at least two-thirds of the senators find the president guilty, he is removed, and the vice president takes over as president.
What are the rules?
There are no standard rules. Rather, the Senate passes a resolution first laying out trial procedures.
“When the Senate decided what the rules were going to be for our trial, they really made them up as they went along,” said Greg Craig, who helped defend Mr. Clinton in his impeachment proceeding and later served as White House counsel to President Barack Obama.
“参议院决定我们的审讯采用哪些规则时，的确是且行且定，”曾在克林顿弹劾案中为其辩护、后来给贝拉克·奥巴马（Barack Obama）总统当过白宫法律顾问的格雷格·克雷格（Greg Craig）表示。
For example, Mr. Craig said, the initial rules in that case gave four days to the Republican managers to make a case for conviction, followed by four days for the president’s legal team to defend him — essentially opening statements. The Senate then decided whether to hear witnesses, and if so, whether it would be live or on videotape. Eventually, the Senate permitted each side to depose several witnesses by videotape.
The rules adopted by the Senate in the Clinton trial — including limiting the number of witnesses and the length of depositions — made it harder to prove a case compared with trials in federal court, said former Representative Bob Barr, a Georgia Republican who served as a House manager during the trial and is also a former United States attorney.
“Impeachment is a creature unto itself,” Mr. Barr said. “The jury in a criminal case doesn’t set the rules for a case and can’t decide what evidence they want to see and what they won’t.”
What are the standards?
The Constitution says a president allows impeachment and removal for “treason, bribery, or other high crimes and misdemeanors.” But no controlling authority serves as a check on how lawmakers choose to interpret that standard, which makes it as much a question of political will as of legal analysis.
In the case of Mr. Clinton’s trial, for example, Robert Byrd, a Democratic senator from West Virginia at the time, told his colleagues that he thought Mr. Clinton was clearly guilty of perjury but that removing him from office was a bad idea.
“To drop the sword of Damocles now, given the bitter political partisanship surrounding this entire matter, would only serve to further undermine a public trust that is too much damaged already,” he said. “Therefore, I will reluctantly vote to acquit.”
Mr. Clinton was impeached by a Congress in which the opposition party controlled both the House and the Senate. In Mr. Trump’s case, his party controls both chambers, making it more politically unappealing for them to vote to impeach him.
What about the 25th Amendment?
Adopted in 1967, the 25th Amendment provides another mechanism for removing a president. It is geared toward dealing with a president who becomes disabled from carrying out the duties of the office, as opposed to presidential lawbreaking.
Under its procedures, if both the vice president and a majority of the cabinet tell Congress that the president is “unable to discharge the powers and duties of his office,” the vice president immediately becomes the acting president. If the president contests that finding, but two-thirds of both chambers of Congress side with the vice president, he remains the acting president for the remainder of the term.