House Intel Committee leader/Friend of Moby Rep. Adam Schiff paused the impeachment hearing featuring testimony from ousted US ambassador to the Ukraine and 30-year career diplomat Marie Yovanovitch to read the president's tweet reactions to the hearing. In her opening statement, Yovanovitch described her shock at the embrace by top USA officials of a smear campaign that ultimately led to her ouster.
They have also accused him of withholding aid to Ukraine to pressure Mr Zelensky into launching an investigation.
As she was testifying, Trump tweeted an attack on Yovanovitch, saying he had every right to remove her.
After the hearing, Stefanik informed Democrats that this was "not a hearing about tweets".
"Quid pro quo: Bribery", Pelosi said about Trump's July 25 phone call in which he asked Ukrainian President Volodymyr Zelensky for a favour.
Schiff replied: "Well, I want to let you know, ambassador, that some of us here take witness intimidation very, very seriously".
Democratic committee chairman Adam Schiff said in his opening statement: "The powers of the presidency are vast, but they are not absolute and can not be used for a corrupt goal".
"We're in Chapter 1 of a process", said Rep. Raja Krishnamoorthi, Democrat of IL, and a member of the intelligence committee conducting the inquiry.
President Trump has denied the accusation.
The money, approved by the US Congress to help US ally Ukraine combat Russia-backed separatists, was later provided to Ukraine. "I have freedom of speech, just as other people do".
The investigation threatens to make Trump the third United States president to be impeached, after Andrew Johnson in 1868 and Bill Clinton in 1998, although the Senate - where Republicans enjoy a majority - would need to convict him to remove him from office. Republicans have offered no evidence of corruption by former vice president Biden or his son. Schiff asked, prompting Yovanovitch to defend her past work.
Asked during her closed-door deposition if anyone at the State Department who was alerted to Giuliani's role tried to stop him, she testified, "I don't think they felt they could". "I still find it hard to comprehend that foreign and private interests were able to undermine USA interests in this way".
At the opening of the hearing, Republican Devin Nunes criticised Democrats for launching the impeachment inquiry, calling it a political exercise based on second- and third-hand hearsay.
It raises questions about why Mr Trump didn't talk about corruption or endorse Ukraine's territorial integrity in the call, particularly given Ukraine's history of prosecutorial misconduct and Russian support for insurgents fighting Ukrainians in the nation's eastern border region.
Democrats on the House Intelligence Committee have been thanking Yovanovitch for her bravery and her service. And, more surprisingly, Baier seemed to take Yovanovitch's side as well. Holmes himself might testify in public.
Ms Yovanovitch said events in Ukraine should concern USA politicians.
While Trump applauded the aggressive stance of some of his Republican defenders, he felt that numerous lawmakers in the opening hearing could have done more to support him and he pressed that case with congressional allies ahead of Friday, according to Republicans who were not authorized to speak publicly about private conversations and were granted anonymity.
More public hearings are scheduled for next week.