The former American ambassador to Ukraine has told the impeachment hearing in the US of the "big threat" she felt upon being ousted from her post and learning that Donald Trump had denounced her in a phone call with Ukraine's president.
The hearing before the House Intelligence Committee heard that in the call in July, Mr Trump criticised Marie Yovanovitch as "bad news" and said she was "going to go through some things".
In an extraordinary moment, Mr Trump himself went after her again as she spoke, tweeting from the White House that everywhere she served had "turned bad".
He emphasised that as president he had the "absolute right" to appoint his own ambassadors.
His attack on an impeachment witness during her testimony has drawn a furious response from Democrats, who accused him of witness intimidation, and even some allies criticised him.
"Witness intimidation is a crime," US senator and presidential contender Kamala Harris wrote on Twitter after Mr Trump wrote that everywhere former US ambassador Marie Yovanovitch went in her long career "turned bad".
Mr Trump lashed out at Ms Yovanovitch on Friday as she was testifying on the second day of televised hearings in the US House of Representatives intelligence committee impeachment inquiry, which threatens the Republican president even as he seeks re-election next year.
"The president is smearing the anti-corruption ambassador as she testifies against him," said Democratic Representative Eric Swalwell.
"This lie is an effort to discredit her and chill others who may have the courage to testify against him. This is open-and-shut consciousness of guilt. He keeps acting guilty."
House intelligence committee chairman Adam Schiff read Mr Trump's tweet out to Ms Yovanovitch during the hearing and asked for her response.
"I can't speak to what the president is trying to do, but I think the effect is to be intimidating," she said.
Mr Schiff replied: "Well, I want to let you know, ambassador, that some of us here take witness intimidation very, very seriously."
Other Democratic committee members expressed outrage.
Fox News, which consistently supports Mr Trump, was critical of his Twitter attack on Friday, with anchors and guests saying Ms Yovanovitch was a credible witness and the tweets were ill-advised.
"There is no way to put lipstick on this porcine situation," said Ken Starr, a conservative commentator and the special prosecutor in the investigation that led to impeachment charges against Democratic president Bill Clinton in 1998.
But Republican Representative Jim Jordan dismissed a reporter's suggestion that Mr Trump's tweeting during the testimony might not be helpful to Republicans on the committee.
"Look, the president has been frustrated with this relentless attack on him that started even before he was president," Mr Jordan said. "I think that's what drives that."
Asked to comment on Democratic claims of witness intimidation, Mr Jordan said: "The witness is testifying. She wouldn't even have known about the quote if Mr Schiff hadn't read the tweet."
Doug Heye, a Republican strategist who often criticises Mr Trump, said the tweet would do little to sway public opinion on the hearings.
"The battle lines have largely been drawn and people have made up their minds. The problem for Trump here is that, instead of being a counterpuncher he claims to be, he simply always takes the bait," Mr Heye said.
"We learned a long time ago that despite the wishes of even his own staff, Trump is never going to simply stop tweeting."
