WASHINGTON — A handful of Republican senators tried to stop President Trump from firing Gordon D. Sondland, the ambassador to the European Union who testified in the House impeachment hearings, but the president relieved the diplomat of his post anyway, according to people briefed on the discussions.
The senators were concerned that it would look bad for Mr. Trump to dismiss Mr. Sondland and argued that it was unnecessary, since the ambassador was already talking with senior officials about leaving after the Senate trial, the people said. The senators told White House officials that Mr. Sondland should be allowed to depart on his own terms, which would have reduced any political backlash.
But Mr. Trump evidently was not interested in a quiet departure, choosing instead to make a point by forcing Mr. Sondland out before the ambassador was ready to go. When State Department officials called Mr. Sondland on Friday to tell him that he had to resign that day, he resisted, saying that he did not want to be included in what seemed like a larger purge of impeachment witnesses, according to the people informed about the matter.
Mr. Sondland conveyed to the State Department officials that if they wanted him gone that day, they would have to fire him. And so the president did, ordering the ambassador recalled from his post effective immediately. Mr. Sondland’s dismissal was announced just hours after another impeachment witness, Lt. Col. Alexander S. Vindman, and his twin brother, Lt. Col. Yevgeny Vindman, were marched out of the White House by security officers and told their services were no longer needed.
The ousters came two days after the Republican-led Senate acquitted Mr. Trump on two articles of impeachment stemming from his effort to pressure Ukraine to incriminate Democratic rivals. Outraged Democrats called the firings a “Friday night massacre” aimed at taking revenge against government officials who had no choice but to testify under subpoena about what they knew.
Among the Republicans who warned the White House was Senator Susan Collins of Maine, who after voting to acquit Mr. Trump said she thought he had learned a lesson. Others included Senators Thom Tillis of North Carolina, Martha McSally of Arizona and Ron Johnson of Wisconsin. The White House did not respond to requests for comment on Saturday but a senior administration official confirmed the senators’ outreach on behalf of Mr. Sondland, a donor to Mr. Tillis and other Republicans.
Ms. Collins said Saturday that her lesson comment had been misinterpreted and that she had earlier noted that she did not support retribution. “The lesson that I hoped the president had learned was that he should not enlist the help of a foreign government in investigating a political rival,” she said in a statement to The New York Times. “It had absolutely nothing to do with whether or not he should fire people who testified in a way that he perceived as harmful to him.”
The senators did not express the same concern about Colonel Vindman, who is viewed less sympathetically by the president’s allies. Republicans considered some of Colonel Vindman’s comments during his testimony overtly political and, in any case, believed it was untenable for him to remain on the staff of a president with whom he broke so publicly.
Other witnesses who testified have quietly left their positions in recent days. Jennifer Williams, a career official working for Vice President Mike Pence, asked to return early to the Defense Department. Marie L. Yovanovitch, the ambassador to Ukraine removed from her post last spring because she was seen as an obstacle to the president and his associates, retired from the Foreign Service. And her acting successor, William B. Taylor Jr., returned home as well.
Some of these witnesses may begin to speak out. Mr. Taylor has given a series of news media interviews in recent days. And Ms. Yovanovitch has enlisted the Javelin literary agency, picking the same agents who represent John R. Bolton, the former national security adviser, among others.
Mr. Trump on Saturday defended his decision to fire Colonel Vindman, calling the decorated Iraq war veteran “very insubordinate.”
“Fake News @CNN & MSDNC keep talking about ‘Lt. Col.’ Vindman as though I should think only how wonderful he was,” Mr. Trump wrote on Twitter, without explaining why he put the colonel’s rank in quote marks.
“Actually, I don’t know him, never spoke to him, or met him (I don’t believe!),” he continued, “but, he was very insubordinate, reported contents of my ‘perfect’ calls incorrectly, & was given a horrendous report by his superior, the man he reported to, who publicly stated that Vindman had problems with judgement, adhering to the chain of command and leaking information. In other words, ‘OUT’.”
Mr. Trump offered no explanation for why Colonel Vindman’s twin brother, Yevgeny Vindman, who is also an Army lieutenant colonel and who worked as a lawyer on the National Security Council staff, was fired and escorted out of the White House complex at the same time even though he did not participate in the House hearings. Nor did the president mention his decision to recall Mr. Sondland, a hotel magnate who donated $1 million to Mr. Trump’s inaugural festivities before receiving his ambassadorial appointment.
Mr. Sondland and Colonel Vindman were key witnesses in the House hearings. Mr. Sondland, who was deeply involved in the effort to pressure Ukraine, testified that “we followed the president’s orders” and that “everyone was in the loop.” Colonel Vindman, who was on Mr. Trump’s July 25 phone call with Ukraine’s president, testified that it was “improper for the president” to coerce a foreign country to investigate political opponents.
Colonel Vindman, a Ukraine expert on the National Security Council staff, and his brother were scheduled to remain at the White House until July but will now be sent back to the Defense Department. Mr. Sondland, a political appointee, will return to the United States and presumably leave government service.
A lawyer for Colonel Vindman said Mr. Trump’s Twitter messages contained “obviously false statements” about his client.
“They conflict with the clear personnel record and the entirety of the impeachment record of which the president is well aware,” said the lawyer, David Pressman. “While the most powerful man in the world continues his campaign of intimidation, while too many entrusted with political office continue to remain silent, Lt. Col. Vindman continues his service to our country as a decorated, active duty member of our military.”
Mr. Trump’s tweets misstated or overstated testimony about Colonel Vindman. Tim Morrison, who supervised him at the National Security Council for just three months, told the House that he had concerns about Colonel Vindman’s judgment and believed he did not always adhere to the chain of command. But when Mr. Morrison said he had originally heard such concerns from his predecessor, Fiona Hill, she disputed his account.
Ms. Hill, who supervised Colonel Vindman for two years, testified that she had a much narrower concern that he did not have “the political antenna” to deal with matters related to domestic politics. “That does not mean in any way that I was questioning his overall judgment, nor was I questioning in any way his substantive expertise,” she said. “He is excellent on issues related to Ukraine, Belarus and Moldova, on Russian defense issues.”
In fact, Colonel Vindman read from Dr. Hill’s personnel evaluation at his own hearing: “Alex is a top 1 percent military officer and the best Army officer I have worked with in my 15 years of government service. He is brilliant, unflappable, and exercises excellent judgment.”
Democrats on Saturday denounced Mr. Trump’s actions. “By firing Lt. Col. Vindman and Ambassador Sondland like this, the Trump administration signaled it won’t tolerate people who tell the truth,” said Senator Jack Reed of Rhode Island. “The fact that Lt. Col. Vindman’s brother was also removed from the N.S.C., as well as the transfer of Ms. Williams from Vice President Pence’s staff, are signals that the president places blind loyalty above all else, including testimony under oath.”
Peter Baker and Michael S. Schmidt reported from Washington, and Maggie Haberman from New York. Catie Edmondson and Nicholas Fandos contributed reporting from Washington, and Danny Hakim from New York.