Washington — Illinois Congressman Mike Quigley, a Democratic member of the House Intelligence Committee, said President Trump's derogatory remarks about Marie Yovanovitch, the former U.S. ambassador to Ukraine and one of the key witnesses in the impeachment inquiry, are part of a "pattern" of attacks designed to intimidate individuals who may have damaging information about the president.

"When the hearing began and Ambassador Yovanovitch began to testify, I thought, there's no way the Republicans will go after this. If anything, they're going to try to diminish the notion that there was a smear campaign against her," Quigley said on "Face the Nation," referring to Friday's testimony. "And as she was testifying that she felt threatened by the president's remarks, which I understand, the president continues the smear campaign."

The Illinois Democrat said any president has the prerogative to appoint and remove envoys, but he stressed that the actions "can't be part of a corrupt scheme."

"I think that's what we saw here. The fact is, if the president disagrees with you or you don't cheer on the president of the United States, he comes after you and the rule of law is left behind," he said.

In her public testimony on Friday, Yovanovitch, a 33-year diplomat who has served under both Republican and Democratic administrations, described how her ouster was engineered by "foreign corrupt interests" in Ukraine who teamed up with several U.S. citizens, including the president's personal lawyer, Rudy Giuliani, to disseminate information about her that the State Department knew was false.

Yovanovitch detailed how "devastated" she felt when learning that Mr. Trump had said she was "bad news" and would be "going through some things" during his now infamous July call with Ukraine's leader, Volodymyr Zelensky.

Although the White House initially said Mr. Trump would not watch Yovanovitch's hearing, the president took no time to go on the offensive after it started, quickly highlighting on Twitter some of the foreign postings she held during her career.

"Everywhere Marie Yovanovitch went turned bad. She started off in Somalia, how did that go?" the president tweeted as the hearing was underway. "Then fast forward to Ukraine, where the new Ukrainian President spoke unfavorably about her in my second phone call with him."

The tweet was read to Yovanovitch by House Intelligence Committee Chairman Adam Schiff, who asked her how she felt about it. "It is very intimidating," she responded.

Quigley said Mr. Trump's tweet on Friday echoed his attacks against his former personal attorney Michael Cohen, when the latter started cooperating with federal and congressional investigators before going to prison earlier this year. The Illinois Democrat also noted the president has praised his former campaign chairman, Paul Manafort, who is in prison for federal financial crimes and refused to cooperate with federal investigators.

"It's part of a pattern of witness intimidation," Quigley said. "What did he say about Mr. Cohen? That he was a rat. He was talking like a mobster. What'd he say about Mr. Manafort? That he was a good guy because he wasn't cooperating. That's witness intimidation."