In the first formal test of support for the impeachment investigation, the Democratic-controlled House voted almost entirely along party lines - 232 to 196 - to move the probe forward in CongrThe vote allows for public impeachment hearings in Congress, which are expected in the coming weeks and portends a bitter battle ahead as the United States heads into a presidential election year.
Democrats who accuse Trump of abusing his office and jeopardizing national security for personal political gain were almost unanimous in approving Thursday's measure, but they did not pick up a single Republican vote.
"It's a sad day. No one comes to Congress to impeach a president," House Speaker Nancy Pelosi said before the vote.
Televised public hearings featuring U.S. officials testifying in Congress about alleged wrongdoing by Trump could crowd out other issues like the economy and immigration as voters turn their minds to the November 2020 election.
That might damage Trump, but some of his supporters say the impeachment drive could actually boost his re-election chances by showing him at loggerheads with Washington-based political foes.
Republicans accused Democrats of using impeachment to overturn the results of his 2016 election victory.
Trump told a UK radio station the Democrats knew they were losing next year's vote and so were trying to take him down.
"The Democrats are desperate, they're desperate. They have nothing," Trump told LBC Radio in an interview. White House spokeswoman Stephanie Grisham denounced the process as "unfair, unconstitutional and fundamentally un-American."
A number of opinion polls ahead of next year's election show several leading Democratic presidential candidates leading Trump.
The probe focuses on a July 25 telephone call in which the U.S. president asked his Ukrainian counterpart, Volodymr Zelenskiy, to investigate Trump's Democratic political rival Joe Biden, a former U.S. vice president, and his son Hunter, who had served as a director for Ukrainian energy company Burisma.
Biden is a leading candidate in the Democratic presidential nomination race to face Trump in 2020. He and his son deny any wrongdoing.
Trump has also denied wrongdoing. Republicans have largely stuck by him, blasting the impeachment push as a partisan exercise that has given them little input.
Thursday's vote showed that Democrats have enough backing in the House to later bring formal charges, known as articles of impeachment, if they feel they have enough evidence.
"It should not be Nancy Pelosi and a small group of people that she selects that get to determine who is going to be our president," said Kevin McCarthy, the top House Republican.
Just two Democrats - Collin Peterson of Minnesota and Jeff Van Drew of New Jersey - broke with their party and voted against the measure. Both represent districts where Trump won in 2016. Other Democrats from Trump-leaning districts, such as Jared Golden of Maine, voted yes.
Representative Justin Amash, who left the Republican Party this year and is now an independent, voted for the measure.
If the House eventually votes to impeach Trump, that would set up a trial in the Republican-controlled Senate. Trump would not be removed from office unless the Senate votes to convict him by a two-thirds margin, something that looks unlikely as congressional Republicans have been reluctant to move against the president.
The U.S. Constitution gives the House broad authority to set ground rules for an impeachment inquiry and Democrats say they are following House rules on investigations.
The investigation is probing whether Trump misused the power of his office and, if so, whether that amounted to "high crimes and misdemeanors" that merit impeachment and removal from office under the Constitution.
Democratic leaders in Congress declined to say when public hearings would start, but they are expected to begin in the next few weeks. The inquiry has so far taken place behind closed doors in front of House committee members.
Current and former Trump administration officials have testified that the White House went outside normal diplomatic channels to pressure Zelenskiy to investigate the Bidens.
The top U.S. diplomat in Ukraine, William Taylor, said Trump held back nearly $400 million in security aid in an attempt to get Zelenskiy to publicly declare that he would carry out the investigations that the U.S. president sought - a "quid pro quo" confirmed by Trump's acting chief of staff, Mick Mulvaney.
Lawmakers leading the inquiry on Thursday heard closed-door testimony from Tim Morrison, the top Russia specialist on Trump's National Security Council. Morrison resigned from his position on Wednesday.
Morrison backed up the testimony of other witnesses who said the White House attempted to pressure Ukraine, according to a congressional source. He said he learned of the effort from one of those involved, a Trump donor named Gordon Sondland who serves as the U.S. ambassador to the European Union.
Morrison did not criticize Trump directly, however, and said that he did not think anything illegal was discussed on the July 25 call, the congressional source said.
Republican U.S. Representative Mark Meadows said Morrison's testimony had been "very damaging" to the case for impeachment.
"If any witness would suggest that the impeachment resolution that was passed earlier today should come to a screeching halt, it was this witness," Meadows told reporters, without elaborating on Morrison's deposition.
Committee members have asked a prominent player, former national security adviser John Bolton, to appear next week. Others have testified that Bolton was alarmed by a White House effort to pressure Zelenskiy. Bolton's lawyer has said he is not willing to testify unless a subpoena is issued.