The Republicans also accused committee Democrats of lacking transparency and hiding information from the American people.
Here's a guide to who is testifying, what they'll be asked about and why it matters.
Public hearings in the House impeachment inquiry are set to begin. Unlike previous hearings, such as those relating to the final report of the special counsel Robert Mueller, this time lawyers, not committee members, will do the bulk of the questioning.
Democrats are likely to call further witnesses after this week.
The House Intelligence Committee on Wednesday will first hear from William Taylor, the top USA diplomat in Ukraine. But he railed against his critics on Twitter, even accusing House Democrats of "doctoring" transcripts of impeachment witnesses without evidence to back up his claim. He was ambassador to Ukraine from 2006 to 2009. Biden is a leading contender for the Democratic nomination to face the Republican president in the 2020 election.
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Last week, lawmakers grilled Muilenburg about his $23.4 million compensation, including a $13.1 million incentive bonus in 2018. Both crashes have been attributed to an automated system known as MCAS, or Maneuvering Characteristics Augmentation System.
Former Special Envoy to Ukraine Kurt Volker departs following a closed-door deposition led by the House Intelligence Committee on Capitol Hill in Washington on October 3, 2019.
Hers is the latest transcript to be made public that showed the internal machinations of the administration as Mr Trump insisted that almost $US400 million ($585 million) in aid slated for Ukraine be withheld until its President Volodymyr Zelenskiy publicly launched an investigation into former USA vice-president Joe Biden - one of Mr Trump's top domestic political rivals.
Taylor's testimony in the closed sessions has been considered among the most damaging to the president. His son Hunter Biden served on the board of a Ukrainian energy company called Burisma. She told investigators that the departments working on Ukraine aid were unified in their view "that this assistance was essential" and in "trying to find ways to engage the president" to free the funding once they realized it had been frozen.
US diplomats have testified before Congress behind closed doors that the president's political appointees and his personal attorney, Rudy Giuliani, were attempting to trade a White House meeting for the public announcement of investigations into the Bidens and any role Ukraine had in election interference in the 2016 presidential election.
Also on Monday, acting White House Chief of Staff Mick Mulvaney withdrew a motion to join a lawsuit seeking to have a judge settle whether he can be compelled by Congress to testify in the inquiry.
"I had been making, and continue to make, this point to all of my Ukrainian official contacts".
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A third SUV - about 10 miles behind the other two - had been headed to an airport in Arizona, Miller said. Relatives and Mexican soldiers found the girl after searching the area for about two hours, Miller said.
"Somehow an effort that he was engaged in to see if there was a statement that the government of Ukraine would make", she said, "that would somehow disavow any interference in US elections and would commit to the prosecution of any individuals involved in election interference".
Whether the public testimony of multiple career diplomats changes that is not clear. Kent said the effort to smear Yovanovitch was part of a "campaign of lies" by Giuliani.
"It's impossible to bring this case forward in my view fairly without us knowing who the whistleblower is and having a chance to cross examine them about any biases they may have", said Republican Sen.
The whistleblower's account has largely been confirmed by testimony and other evidence. First, they believe that the process of impeaching a president requires a completed probe.
A third line of questioning may lead to another defence - that what took place between the Trump administration and Ukraine, while distasteful, doesn't rise to the level of "high crimes and misdemeanours", the constitutional standard for impeachment. Only a basic majority of the 435 member House is required to approve impeachment. If so, the next step would be a trial in the Senate.
Will public hearings change minds? Among them are Lt. -Col.
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Anything other than a win and it is still game-on for both teams. It was quite similar to the Champions League game. This is now more than a football match.
Following the release of the most recent transcripts, Trump tweeted that he would release the transcript of the of the "first" and "therefore most important" phone call he had with Zelenskyy. Democrats from the House would act as the prosecuting team, while Trump's lawyers would defend him, and Trump could argue in his own favor.