In an accelerating assault on Donald Trump’s critics in the days since his impeachment acquittal, the administration fired Gordon Sondland, the ambassador to the European Union, shortly after removing Lt Col Alexander Vindman from his White House post on Friday.

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Sondland and Vindman delivered damaging testimony during the impeachment inquiry, in defiance of Trump.

“I was advised today that the president intends to recall me effective immediately as United States Ambassador to the European Union,” Sondland said in a statement.

Hours earlier, Vindman, a Ukraine expert on the national security council who had been scheduled to rotate out of his White House assignment this summer, was suddenly fired and escorted out of the building on Friday, according to a statement from his lawyer.

The attorney, David Pressman, said: “He followed orders, he obeyed his oath, and he served his country. And for that, the most powerful man in the world – buoyed by the silent, the pliable, and the complicit – has decided to exact revenge.

“There is no question in the mind of any American why this man’s job is over, why this country now has one less soldier serving it at the White House. Vindman was asked to leave for telling the truth.”

Sondland and Vindman’s firings were the latest in a string of moves by Trump against his perceived antagonists from the impeachment inquiry.

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An hour after Trump’s acquittal, Senate Republicans announced an investigation of Hunter Biden, whose former employment with a Ukrainian gas company Trump has made the centerpiece of a political attack on his father, Joe Biden, the former vice-president. Trump and his son Donald Trump Jr have also repeatedly attacked Mitt Romney of Utah in the past week, the only Republican senator to vote to convict Trump on abuse of power. Romney voted to acquit Trump on obstruction of Congress.

Central to the House impeachment managers’ argument for Trump’s removal was a warning that if he faced no retribution for his misconduct, Trump would expand the pace and scope of his power abuses.

The president’s son, Donald Trump, Jr, seemingly confirmed that Sondland and Vindman’s removal was in retaliation for their cooperation with the Democrats’ investigation. Were it not for the lead impeachment manager Adam Schiff’s “crack investigation skills”, the president “might have had a tougher time unearthing who all needed to be fired”, he wrote in a tweet.

Sondland’s bombshell testimony was a turning point in the impeachment inquiry. Asserting that he and other officials “followed the president’s orders” to negotiate a quid pro quo with Ukraine, Sondland implicated Trump and several other senior officials.

Facebook Twitter Pinterest Gordon Sondland testifies before the House intelligence committee on Capitol Hill in November. Photograph: Andrew Harnik/AP

After initially denying a pressure campaign in Ukraine, Sondland revised his testimony, admitting that he told a senior official in Ukraine that nearly $400m in US aid hinged on an announcement that the country was investigating Trump’s political rivals.

Sondland also said that an Oval Office meeting with Trump depended on Ukranian officials publicly declaring investigations into Burisma, a gas company linked to the 2020 presidential candidate Joe Biden’s son, Hunter, and an unsubstantiated conspiracy theory that Ukraine planted evidence on a Democratic party server to make it appear that Russia interfered in the 2016 election.

Throughout his shocking televised testimony, Sondland remained calm, even jovial. When, during his questioning, he was told that another witness referred to him as “the Gordon problem”, Sondland responded: “That’s what my wife calls me.”

The wealthy hotelier and Trump donor, who has been described as one of the so-called “three amigos” who bypassed usual state department channels in Ukraine, had no foreign policy experience prior to his appointment as ambassador.

Most of the dozen witnesses who testified in public impeachment hearings had already left their posts in the Trump administration before testifying. But both Sondland and Vindman continued to work in the administration after they testified about Trump’s Ukraine scheme.

A line from Vindman’s testimony about the supposed strength of the rule of law in the United States – “here, right matters” – became a refrain in the prosecution of Trump at the Senate impeachment trial, which ended on Wednesday.

Schiff, urged the senators to reflect on Vindman’s words as they weighed the charges against Trump. Trump was acquitted on both articles of impeachment on a party-line vote, with the exception of Romney’s vote to convict on abuse of power.

In the opening statement that Vindman gave when testifying to the House of Representatives last October, he outlined how he planned to describe his concerns that the president’s plot to weaken rival Biden by strong-arming the Ukrainian government into investigating him was undermining US foreign policy in Ukraine.

Alexander Vindman's Trump-Ukraine testimony: five key takeaways Read more

Vindman’s testimony was a dramatic moment in the inquiry. At one point he delivered a message to his father, who fled the former Soviet Union with the family to settle in New York.

“Dad, my sitting here today, in the US Capitol talking to our elected officials is proof that you made the right decision 40 years ago to leave the Soviet Union and come here to the United States of America in search of a better life for our family,” he said.

“Do not worry. I will be fine for telling the truth.”

Why do you have the confidence to “tell your dad not to worry?” Representative Sean Maloney asked Vindman.

“Congressman, because this is America,” he replied, without hesitating. “This is the country I have served and defended, that all of my brothers have served. And here, right matters.”

Schiff echoed Vindman’s words once more in response to the news of his firing. “He upheld his oath when others would not,” Schiff said in a tweet. “Right matters to him. And to us.”