Trump has denied any wrongdoing, derided some of the current and former United States officials who have appeared before committees as "Never Trumpers" and branded the investigation a witch hunt aimed at hurting his re-election changes. But the White House's acting chief of staff thought otherwise.
The first public hearings in the House Democrats' ongoing impeachment inquiry into President Trump's requests for Ukraine to investigate his political rivals begin Wednesday in Washington, D.C., with William Taylor, the top us diplomat in Ukraine, and George Kent, a senior State Department official, scheduled to testify in an open session at 10 a.m. ET. Taylor took his concerns about Trump's alleged attempt to extort Ukraine, he said, to both national security adviser John Bolton and to secretary of state Mike Pompeo. The Constitution sets a dramatic, but vague, bar for impeachment, and there's no consensus yet that Trump's actions at the heart of the inquiry meet the threshold of "high crimes and misdemeanours".
The full House could proceed to a vote on the impeachment of Trump by the end of the year.
US Representative Jim Himes speaks to the media after attending a closed meeting for members of Congress at the US Capitol in Washington.
But when the Democratic chair Adam Schiff gavels the House intelligence committee to order, cameras from every major network will carry the proceedings to millions of Americans, some of whom will be encountering the allegations against Trump for the first time.
Schiff called it a "solemn undertaking", and counselled colleagues to "approach these proceedings with the seriousness of goal and love of country that they demand".
"When it comes to impeachment, the framers dedicated a significant amount of time to thinking about this", Brettschneider said. Mr Biden is a leading contender for the Democratic nomination for the 2020 presidential election.
Trump calls the whole thing a "witch hunt", a retort that echoes Nixon's own defence. Republicans say Trump had good reasons for stalling aid and acted within his power to do so.
Democratic House Speaker Nancy Pelosi was initially reluctant to launch a formal impeachment inquiry.
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Many groups studying the outbreak have mentioned vitamin E, she says, but have not found it in every single sample as the CDC did. The Department of Health also asks retailers to immediately stop selling vapor products known to contain vitamin E acetate .
But the next day Trump got on the phone.
House Republicans released their list on Saturday of witnesses they would like brought before the committee, including Mr Hunter Biden and the yet-unnamed whistleblower who first brought the complaint against Mr Trump over his July 25 call with Ukrainian President Volodymyr Zelenskiy.
Kent, who has been in the foreign service since 1992, now oversees policy for a number of eastern European nations, including Ukraine.
President Trump has repeatedly claimed his call was "perfect" and has cited as proof a "transcript" of it that was made public subsequently. Democrats fought for the letter to be released to them as required.
He is the fourth USA president to face impeachment.
In another unusual move, Republicans have taken the step of adding Representative Jim Jordan to the House Intelligence Committee, replacing Representative Rick Crawford, so Jordan can question witnesses. Pelosi, given the nod from her most centrist freshman lawmakers, opened the inquiry.
Democrats, who control the House, have argued that Trump abused his power in pressing a vulnerable USA ally to carry out investigations that would benefit Trump politically.
In his testimony last month, Taylor - America's top diplomat in Kyiv - implied that two Zelensky aides blamed Ukraine, rather than Russian Federation, for the long-running, bloody war in the eastern part of the country. Later this week, former US ambassador to Ukraine Marie Yovanovich will appear. He joined the State Department in 1992.
The hearing is expected to conclude between 2:30 p.m. and 4:30 p.m. ET, when the witnesses are dismissed by the chairman.