Speaker of the US House of Representatives Nancy Pelosi has begun a formal impeachment inquiry into President Trump over allegations that he pressured a foreign power to damage a political rival.
Ms. Pelosi said on Tuesday evening that Donald Trump “must be held accountable”.
Mr. Trump has said he did nothing wrong, calling the move in the Democratic-controlled House “ludicrous” and a “witch hunt”.
The high-stakes move by Ms. Pelosi was prompted by allegations that Mr. Trump pressured the Ukrainian president to investigate his leading political rival, former Democratic Vice-President Joe Biden.
Analysts say the stage has now been fully set for a potentially explosive stand-off between Democrats and the Republican president, ahead of the November 2020 election.
If, as expected, an impeachment vote is carried through the House, Mr. Trump becomes only the third president in US history to have been impeached, behind Republican Richard Nixon and Democrat Bill Clinton.
But the proceedings would likely then meet a brick wall in the Senate, where his Republican Party holds enough seats to prevent him from being removed from office by at least sixty of the 100 members.