Donald Trump joins a small group of fellow presidents now that he's the subject of an official impeachment inquiry in the House of Representatives. Only three of his predecessors underwent similar proceedings: Andrew Johnson and Bill Clinton, who were acquitted after trials in the Senate, and Richard Nixon, who resigned to avoid being impeached in the Watergate scandal.
What is the process and the purpose?
The rarely used procedure is spelled out in Article II, Section 4 of the Constitution, which stipulates that the president and other officers of government "shall be removed from office on impeachment for, and conviction of, treason, bribery, or other high crimes and misdemeanors."
The first step toward impeachment is taken by the House, which debates and votes on whether to bring charges.
This can be done by a simple majority of the House's 435 members.
If the House adopts an impeachment resolution, the Senate then holds a trial, with the chief justice of the U.S. Supreme Court presiding. A two-thirds majority vote is required in the Senate to convict and remove a president - an outcome that has yet to occur.
Only 20 government officers in all, including Johnson and Clinton, have been impeached, and only eight of them, all federal judges with lifetime tenure, have been convicted and removed from office.
Trump's political future
Fifty-eight floors above Manhattan, President Donald Trump watched his legacy change and his political future grow more uncertain. The president, back in his hometown of New York for the U.N. General Assembly, was taking "executive time" at his Trump Tower penthouse late Tuesday afternoon when Speaker Nancy Pelosi announced that the House was launching a formal impeachment inquiry against him.
Pelosi's move increases the odds that Trump will become the third U.S. president to be impeached.
Trump and his advisors called it a positive move, which could work against the Democrats. The president himself said the move could help his electoral chances, but he reacted in the moment with a cascade of angry tweets that accused Democrats of engaging in "a witch hunt" and "presidential harassment."
"They're going to lose the election, and they figure this is a thing to do," Trump told reporters. Speaking of Pelosi, he added, "If she does that, they all say that's a positive for me, for the election. You could also say, 'Who needs it? It's bad for the country.'"
The call that adds fuel to the fire
The impeachment enquiry comes on the back of a whistleblower complaint accused him of pressuring the leader of Ukraine to dig up damaging material about political foe Joe Biden's family.
The revelations revolve in part around a July 25 phone call the president had with Ukrainian President Volodymyr Zelenskiy in which Trump is said to have asked for help investigating Biden and his son Hunter.
In the days before the call, Trump ordered advisers to freeze $400 million in military aid for Ukraine, prompting speculation that he was holding up the money as leverage for information on the Bidens. Trump has denied that charge but acknowledged he blocked the funds.
Trump recounted the call, saying he told President Volodymyr Zelensky that "we don't want our people like Vice President Biden and his son [adding to] the corruption already in the Ukraine." On Tuesday Trump said he would release a "complete, fully declassified and unredacted transcript " of the call.
Hunter Biden, son of Joe Biden, served on the board of a Ukrainian gas company at the same time his father was leading the Obama administration's diplomatic dealings with Kyiv. Though the timing raised concerns among anti-corruption advocates, there has been no evidence of wrongdoing by either the former vice president or his son.
Trump approved release of the "unredacted" transcript. "You will see it was a very friendly and totally appropriate call," he tweeted between meetings at the United Nations. "No pressure."
"... the president's betrayal of his oath of office"
On Wednesday, the House is expected to consider a symbolic but still notable resolution insisting the Trump administration turn over to Congress the whistleblower's complaint. The Senate, in a rare bipartisan moment, approved a similar resolution Tuesday.
The lawyer for the whistleblower, who is still anonymous, released a statement saying he had asked Trump's director of national intelligence to turn over the complaint to House committees and asking guidance to permit the whistleblower to meet with lawmakers.
Pelosi suggested that this new episode - examining whether a president abused his power for personal political gain - would be easier to explain to Americans than some of the issues that arose during the Mueller investigation and other congressional probes.
The speaker put the matter in stark terms: "The actions of the Trump presidency revealed dishonorable facts of the president's betrayal of his oath of office, betrayal of his national security and betrayal of the integrity of our elections."
The Republican-controlled House voted in October 1998 to begin impeachment proceedings against Clinton after months of controversy over his relationship with White House intern Monica Lewinsky.
That vote was triggered by two rounds of testimony given by Clinton earlier in the year. In January, he denied having a sexual relationship with Lewinsky" in August, under questioning from independent counsel Kenneth Starr before a federal grand jury, he testified that he engaged in an inappropriate relationship with Lewinsky.
Clinton was impeached on Dec. 19, 1998, on the grounds of perjury to a grand jury and obstruction of justice. A Senate trial against Clinton commenced on Jan. 7, 1999, and unfolded over four weeks, with Chief Justice William Rehnquist presiding.
On Feb. 12, the Senate voted to acquit Clinton on both charges - falling far short of the 67 votes needed to convict. Only 45 senators voted for conviction on the perjury charge, and 50 for the obstruction charge.
The House initiated an impeachment process against Nixon in February 1974, authorizing the Judiciary Committee to investigate whether grounds existed to impeach him of high crimes and misdemeanors. The charges mostly related to Watergate - shorthand for the 1972 break-in at the Democratic National Committee headquarters and the Nixon administration's attempts to cover up its involvement.
In July 1974, the Judiciary Committee approved three articles of impeachment against Nixon - for obstruction of justice, abuse of power and contempt of Congress.
Before the full House could vote on the articles of impeachment, a previously undisclosed audio tape was released that made clear Nixon had a role in the cover-up. He resigned from office on Aug. 9, 1974.
Johnson's impeachment in 1868 was the culmination of a bitter dispute between the president and the Republican-controlled House over Reconstruction following the Civil War.
The specific trigger for impeachment was Johnson's attempt to fire Secretary of War Edwin Stanton, who favored a tougher approach than Johnson toward the defeated South. Nine of 11 impeachment articles concerned the head of the War Department.
The House voted to impeach Johnson on March 3, 1868. Three days later, the Senate convened a formal impeachment trial, with Supreme Court Chief Justice Salmon P. Chase presiding.
On May 16, after an often-stormy trial, the Senate failed to convict Johnson on one of the 11 articles, falling short of the necessary two-thirds majority by one vote. After a 10-day recess, two more votes failed by the same margin, and the trial was adjourned.
After Pelosi's Tuesday afternoon announcement, the president and his reelection team swung into high gear, releasing a series of tweets attacking Democrats, including a video of presidential critics like the speaker and Rep. Ilhan Omar discussing impeachment. It concluded with a message for the Trump base: "While Democrats 'Sole Focus' is fighting Trump, President Trump is fighting for you."
A lot depends on the transcript that is to be released on Wednesday, to prove the allegations false. The burden will probably now shift to Democrats to make the case to a scandal-weary public.
In a highly polarised Congress, an impeachment inquiry could simply showcase how clearly two sides can disagree when shown the same evidence rather than approach consensus.
Building toward this moment, the president has repeatedly been stonewalling requests for documents and witness interviews in the variety of ongoing investigations. Maybe, after this move, the White House will respond favourable to information and document requests from the Congress as Trump gears up for his next electoral bout with the people of America.
- Inputs from agencies