Democrats in the US House of Representatives have announced formal impeachment charges against President Donald Trump.
The development sets the stage for a battle in the Senate that the White House said would fully exonerate the Republican president.
The two formal charges, or articles of impeachment, accuse Mr Trump of abusing power in his effort to pressure Ukraine to probe a political rival and then obstructing Congress' investigation into the controversy.
The Democratic-controlled House is almost certain to vote to impeach the president. It could take up the matter next week. A trial would then be held in the Republican-controlled Senate, likely in January.
No Republican in either the House or Senate has come out in favour of Mr Trump's removal from office.
House Judiciary Committee Chairman Jerrold Nadler told reporters that Democrats had to take action because Mr Trump had endangered the US Constitution, undermined the integrity of the 2020 election and jeopardised national security.
"No one, not even the president, is above the law," Mr Nadler said at a news conference to announce the formal impeachment charges. He was joined by House Speaker Nancy Pelosi and other Democratic leaders involved in the impeachment probe.
"Our elections are a cornerstone of democracy. ... The integrity of our next election is at risk from a president who has already sought foreign interference in the 2016 and 2020 elections," Mr Nadler said.
Mr Trump has denied wrongdoing and calls the inquiry a hoax.
The White House, which has refused to participate in the hearings in the House because it says the process is unfair, accused Democrats of engaging in a "baseless and partisan" attempt to undo the results of the 2016 election.
"The President will address these false charges in the Senate and expects to be fully exonerated, because he did nothing wrong," White House spokeswoman Stephanie Grisham said in a statement.
After the articles of impeachment were announced, Mr Trump tweeted "WITCH HUNT!" Earlier, he attacked the impeachment effort, tweeting that to impeach a president when the country has such a strong economy "and most importantly, who has done NOTHING wrong, is sheer Political Madness!"
He is the third president to face impeachment.
WITCH HUNT!— Donald J. Trump (@realDonaldTrump) December 10, 2019
Democrats have moved rapidly since launching their inquiry in late September after a whistleblower complaint about a 25 July telephone call in which Mr Trump sought help from Ukrainian President Volodymyr Zelenskiy to investigate former Vice President Joe Biden, a leading contender in the Democratic race to challenge Mr Trump in next November's election.
The abuse of power charge accuses Mr Trump of using nearly $400 million in US security aid and a possible White House meeting with his Ukrainian counterpart to solicit Ukraine to publicly announce the investigations of Mr Biden and a debunked theory that Ukraine, not Russia, interfered in the 2016 US election.
The obstruction charge accuses the president of defying and impeding the House's efforts to investigate the scandal, adding that Mr Trump would remain a threat to the US Constitution if he remained in office.
Representative Adam Schiff, the Democrat who spearheaded the investigation in the House Intelligence Committee, said impeachment was an extraordinary remedy but that Mr Trump had given Democrats no choice.
"The evidence of the president's misconduct is overwhelming and uncontested," Mr Schiff said.
Republicans argue Mr Trump did nothing improper in his call with Mr Zelenskiy and say there is no direct evidence he withheld aid or a White House meeting in exchange for a favour.
Senate Majority Leader Mitch McConnell complained that the impeachment process had delayed work on other matters.
"Obstruction and stalemate have brought us to the 11th hour. I hope ... that both chambers will be able to set aside Democrats' impeachment parade long enough to get the people's business finally finished," he said on the Senate floor.
Democrats sought to counter the argument that impeachment was being done at the expense of passing major legislation.
Democratic Representative Tom Malinowski pointed to upcoming votes in the House on a new trade deal between the United States, Canada and Mexico, two healthcare-related bills, legislation to fund the government through next September, in addition to impeachment, as examples of movement on key issues.
The impeachment battle has divided Americans and raised the heat in an already polarised Congress. No Republican member of Congress has come out in support of impeaching Mr Trump.
The House Judiciary panel will meet later this week to consider the articles of impeachment and make a recommendation on whether to send the formal charges to the full House for a vote, Mr Nadler said.
House Majority Leader Steny Hoyer, the Democrat in charge of scheduling debates on the House floor, told reporters: "I don't want to get ahead of the (Judiciary) Committee, but potentially" the two articles of impeachment will be debated on the House floor next week.