A pivotal but largely forgotten player in the last presidential impeachment effort suddenly made an unexpected appearance Wednesday in the latest one, this time in a radically different role.

On one of the most tumultuous days in congressional history — Dec. 19, 1998 — days before he was expected to claim the speaker’s gavel, Rep. Bob Livingston (R-La.) admitted to an extramarital affair and announced his resignation hours before the House voted to impeach President Bill Clinton for conduct related to Clinton’s own affair.

Now a prominent Washington lobbyist, Livingston has emerged nearly 21 years later as a behind-the-scenes player in the impeachment investigation of President Trump, allegedly urging at least one Trump administration official to oust the U.S. ambassador to Ukraine whose removal is a key episode in the probe.

Livingston’s role in pushing out the envoy was first revealed in testimony delivered Wednesday by State Department official Catherine M. Croft.

Livingston did not respond to messages seeking comment sent through his firm, the Livingston Group. Lobbying records indicate he has worked for multiple entities with ties to former Ukrainian prime minister Yulia Tymoshenko, who lost a presidential bid earlier this year.

Croft’s prepared testimony portrays Livingston as a player in a multifront effort to force the ouster of the ambassador, Marie Yovanovitch, and install a new envoy more sympathetic to Trump. Yovanovitch was ultimately recalled in June, and her removal is among several key episodes in the impeachment investigation, which is probing allegations that Trump tied the delivery of U.S. military aid to Ukraine investigating certain political targets, including the son of former vice president and 2020 presidential candidate Joe Biden.

Croft describes receiving “multiple calls” from Livingston urging Yovanovitch’s firing during her time detailed to the National Security Council as a director from August 2015 to July 2017.

“He characterized Ambassador Yovanovitch as an ‘Obama holdover’ and associated [her] with George Soros,” she said in a written statement obtained by The Washington Post. “It was not clear to me at the time — or now — at whose direction or at whose expense Mr. Livingston was seeking the removal of Ambassador Yovanovitch.”

Croft said she relayed those contacts to her supervisor, NSC senior director Fiona Hill, and George Kent, a senior State Department official. Both have already testified in the House inquiry. Croft testified that she is “not aware of any action that was taken in response.”

Livingston’s motivation for wanting Yovanovitch removed is not fully known. But according to lobbying records, he has a key business relationship with Tymoshenko, a gas mogul who has been on a years-long quest to regain political power in Ukraine after she lost the prime ministership in 2010. Part of that quest has been to build relationships in the U.S. with key government officials to burnish her reputation as a reformer despite suspicions of corruption in her home country.

Two groups with ties to Tymoshenko — Association of Enterprises Ukrmetalurgprom and Innovative Technology & Business Consulting — have both hired the Livingston Group, tapping a firm with a long record of representing foreign clients including the governments of Iraq, Egypt and Turkey.

The firm was first hired by Ukrmetalurgprom, a steel industry trade group, in April 2018 for a three-month period and then again in September 2019 on a one-year contract at a $20,000-a-month retainer. And in June 2018, Innovative Technology & Business Consulting hired Livingston’s firm for a $50,000-a-month retainer for a year.

Livingston’s firm played a key role in arranging a visit that Tymoshenko made to Washington in December, during which she met with administration and congressional officials.

In the months ahead of the visit, Livingston and his colleagues contacted the offices of about two dozen prominent House and Senate members, including the Republican chairmen of the committees dealing with intelligence and foreign affairs in both chambers, as well as Kevin McCarthy (R-Calif.), then the House majority leader, and Sen. Richard J. Durbin (D-Ill.), the Senate minority whip. A key figure in arranging the trip was Christopher Anderson, a State Department official who also testified to House committees Wednesday.

During the early December visit, Livingston accompanied Tymoshenko to meetings with Rep. Adam B. Schiff (D-Calif.), who is now chairman of the House Intelligence Committee and the leader of the impeachment probe, as well as Kurt Volker, the State Department’s special envoy to Ukraine. Volker testified before the House committees earlier this month and described working with Trump lawyer Rudolph W. Giuliani on persuading the new Ukrainian president, Volodymyr Zelensky, to cooperate with Trump’s request for investigations.

Tymoshenko also appeared at think tanks and did media interviews, including for a Wall Street Journal piece in which she promoted her upcoming run for president and cast herself as a pro-Western reformer who could be counted on to counter Russian aggression. She called attacks from pro-Russian groups, including those affiliated with former president Viktor Yanukovych and his political strategist Paul Manafort, “a badge of honor.”

Manafort would later become Trump’s campaign manager until he was embroiled in a Ukrainian corruption scandal himself.

It is unclear whether Livingston was acting in concert or at odds with Tymoshenko to oust Yovanovitch during the time frame Croft describes. A congressional aide knowledgeable about Ukrainian affairs but not authorized to comment publicly said it was possible Tymoshenko viewed Yovanovitch as an obstacle to the resurrection of her domestic political career ahead of the March presidential election.

Yovanovitch was recalled from her position in May after a smear campaign that included unsubstantiated allegations of opposition to Trump that were promoted by Giuliani and amplified by right-wing media outlets and Republican officials, including former Rep. Pete Sessions of Texas. Yovanovitch denied those allegations when she appeared before the House earlier this month.

Whether Livingston’s role is integral to the current impeachment probe remains to be seen.

“I think he sounds rather peripheral, not really central to this, but again, I’m guessing there might be a difference of opinion among my colleagues,” Rep. Stephen F. Lynch (D-Mass.) said Wednesday.

Livingston played a much clearer role in Clinton’s impeachment, helping to push the process forward despite his own doubts in late 1998 as House Republicans warred internally over how to sanction Clinton and what to do about their divisive speaker, Newt Gingrich (R-Ga.).

Livingston launched a bold challenge to Gingrich after Republicans lost seats in the 1998 midterms and was chosen by his party to claim the gavel once the new Congress convened in 1999. But faced with the disclosure of his own extramarital affairs, he decided he could not credibly lead a party pursuing impeachment and announced suddenly on Dec. 19 he would not run for speaker and would resign his seat within months.

“I was prepared to lead our narrow majority as speaker, and I believe I had it in me to do a fine job,” he said in a dramatic floor speech that began with a call for Clinton’s resignation. “But I cannot do that job or be the kind of leader that I would like to be under current circumstances, so I must set the example that I hope President Clinton will follow.”

Since leaving Congress, Livingston has not only been an effective lobbyist but a trusted counselor for many prominent Republican officials. Among them is House Minority Whip Steve Scalise, who holds the suburban New Orleans seat that Livingston once held.

Scalise said Wednesday that Livingston is among a host of Clinton impeachment veterans whom he has spoken to in recent weeks to discuss the practices and procedures surrounding impeachment. But he said Livingston never lobbied him on Ukraine or discussed Yovanovitch with him.

“It’s not uncommon that a new administration removes people from the previous administration and puts in their own folks to carry out their own foreign policy, but I haven’t talked to him about that at all,” Scalise said.

Karoun Demirjian and Tom Hamburger contributed to this report.