President Donald Trump’s Twitter extraordinary attack on an impeachment witness during her testimony has drawn a furious response from Democrats, 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 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.”

Yovanovitch recalls concerted campaign against her

In her testimony, Ms Yovanovitch says she was appalled and devastated when Mr Trump told his Ukrainian counterpart that she “would go through some things” as he put it.

WASHINGTON, DC - NOVEMBER 15: Former U.S. Ambassador to Ukraine Marie Yovanovitch testifies before the House Intelligence Committee in the Longworth House Office Building on Capitol Hill November 15, 2019 in Washington, DC.

Marie Yovanovitch testifies before the House Intelligence Committee in Washington. Photo: AFP

Ambassador Yovanovitch said she was told by a senior Trump administration official there was a concerted campaign against her.

“When I returned to the United States Deputy Secretary of State [John] Sullivan told me there had been a concerted campaign against me and that in fact Mr Trump had been pushing for my removal.

“As Mr Sullivan recently recounted during his Senate confirmation hearing, neither he nor anyone else ever explained or sought to justify the president’s concerns about me.”

She said it was a terrible moment.

Ms Yovanovitch said not all Ukrainians “embraced” US anti-corruption work. “Thus, perhaps, it was not surprising, that when our anti-corruption efforts got in the way of a desire for profit or power, Ukrainians who preferred to play by the old, corrupt rules sought to remove me.

“What continues to amaze me is that they found Americans willing to partner with them and, working together, they apparently succeeded in orchestrating the removal of a US ambassador.

“I do not understand Mr Giuliani’s motives for attacking me,” she said, referring to the president’s personal lawyer Rudy Giuliani, “nor can I offer an opinion on whether he believed the allegations he spread about me … What I can say is that Mr Giuliani should have known those claims were suspect, coming as they reportedly did from individuals with questionable motives and with reason to believe that their political and financial ambitions would be stymied by our anti-corruption policy in Ukraine.”

Ms Yovanovitch said events in Ukraine should concern US politicians. “Ambassadors are the symbol of the United States abroad, they are the personal representative of the president,” Ms Yovanovitch said. “If our chief representative is kneecapped, it limits our effectiveness to safeguard the vital national security interests of the United States.”

– Reuters