WASHINGTON — President Trump on Friday denigrated Marie L. Yovanovitch, the former United States ambassador to Ukraine, even as she testified in the impeachment inquiry about how she felt threatened by Mr. Trump, leading Democrats to accuse him of trying to intimidate a witness in real time.
“Everywhere Marie Yovanovitch went turned bad. She started off in Somalia, how did that go?” Mr. Trump wrote, assailing her on Twitter to his 66 million followers and adding that “It is a U.S. President’s absolute right to appoint ambassadors.”
The president’s insults came as Ms. Yovanovitch told the House Intelligence Committee in powerful and personal terms of the devastation and fear she felt earlier this year, as she was targeted first by Mr. Trump’s allies and later by the president himself during a phone call with President Volodymyr Zelensky of Ukraine. Democrats said Mr. Trump’s onslaught amounted to an attempt to threaten Ms. Yovanovitch, who is still a State Department employee, and other potential witnesses against cooperating with the inquiry, a tactic that they said could itself be impeachable.
Removed from her post as ambassador to Ukraine, Ms. Yovanovitch said she was bereft when she came under fire in the spring from Rudolph W. Giuliani, the president’s personal lawyer, and his eldest son, but even more stunned in September when she learned that Mr. Trump himself had told another foreign leader that she was “bad news” in his now-famous July 25 phone call with Ukraine’s president, and said she would “go through some things.”
“I couldn’t believe it,” said Ms. Yovanovitch, describing her reaction when she saw the transcript of the call, and recounting how the color drained from her face. “Shocked, appalled, devastated that the president of the United States would talk about any ambassador like that to a head of state. And it was me. I couldn’t believe it.”
Representative Adam B. Schiff, Democrat of California and the chairman of the Intelligence Committee, interrupted Ms. Yovanovitch to read the president’s tweet and ask her what she thought. A tight smile on her face, she appeared momentarily uncertain how to respond.
“It’s very intimidating,” she said. She then paused, searching for words. “I can’t speak to what the president is trying to do, but the effect is to be intimidating.”
Mr. Schiff responded in a stern tone that, “Some of us here take witness intimidation very, very seriously.”
Representative Jim Himes, Democrat of Connecticut and a member of the Intelligence Committee, said that Mr. Trump’s attacks on Ms. Yovanovitch amounted to “clear witness tampering” that could be cited in an article of impeachment.
“The president chose to respond to a patriotic and superb public servant with lies and intimidation. Vintage Donald Trump,” Mr. Himes said in a text. “Her boss disparaged and intimidated her not after, but during her testimony.”
Mr. Trump has a history of using his platform to excoriate people who are in a position to serve as witnesses to his own potential wrongdoing, using Twitter and statements at his political rallies to criticize less well-known people by name, in humiliating and sometimes threatening ways.
The tactic functions both as an attempt to discredit his critics, and a warning to deter others from coming forward. At a minimum, it can unleash a cascade of abuse online from Mr. Trump’s supporters. This year, a fervent Trump supporter, Cesar A. Sayoc Jr., was sentenced to 20 years in prison for mailing bombs to people and organizations Mr. Trump had criticized, including prominent Democrats and journalists.
But Friday’s instance, playing out on live television during a public impeachment hearing on Capitol Hill, was a particularly dramatic example.
Mr. Schiff’s framing of Mr. Trump’s behavior as witness intimidation could also have legal and constitutional reverberations at a time when House Democrats are considering an article of impeachment focused on obstruction of Congress and obstruction of justice.
Impeachable offenses can be anything Congress considers an abuse of power, whether or not it also violates a federal criminal statute. But a federal obstruction of justice law, Section 1512 of Chapter 18 of the United States Code, also makes it a felony to harass or intimidate people in an attempt to dissuade them from testifying in an official proceeding.
The obstruction of Congress issues that lawmakers have already been weighing have centered on Mr. Trump’s vow to fight “all” congressional subpoenas, including urging executive branch witnesses to defy lawmakers’ demands that they provide information for its oversight and impeachment investigations.
The obstruction of justice allegations center on Mr. Trump’s attempts to impede the Russia investigation led by the special counsel, Robert S. Mueller III, including in several episodes that also carry overtones of interfering with witnesses.
For example, Mr. Trump bullied Donald F. McGahn II, his former White House counsel, in an attempt to get him to write a memo falsely denying that Mr. Trump had sought to have Mr. Mueller fired. Mr. McGahn had already given a deposition about that earlier episode to the special counsel’s office, so writing such a memo — which he refused to do — would have contradicted and discredited him as a witness.
The Mueller report also recounted how Mr. Trump and his proxies had dangled the prospect of pardons in front of several potential witnesses in the special counsel investigation, while urging them not to “flip” on him and cooperate with prosecutors.
Nicholas Fandos contributed reporting.