Gordon Sondland / REUTERS

U.S. President Donald Trump wasted little time on Friday opening a campaign of retribution against those he blames for his impeachment, firing two of the most prominent witnesses in the House inquiry against him barely 48 hours after being acquitted by the Senate.

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Emboldened by his victory and determined to strike back, Mr. Trump ordered Gordon D. Sondland, the founder of a hotel chain who donated $1 million to the president's inaugural committee, recalled from his post as the ambassador to the European Union on the same day that Lt. Col. Alexander S. Vindman, a decorated Iraq war veteran on the National Security Council staff, was marched out of the White House by security guards, according to The New York Times.

"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 after Colonel Vindman's dismissal. "I am grateful to President Trump for having given me the opportunity to serve, to Secretary Pompeo for his consistent support and to the exceptional and dedicated professionals at the U.S. Mission to the European Union."

Alexander Vindman/ REUTERS

Mr. Sondland and Colonel Vindman were key witnesses in the House impeachment hearings. Mr. Sondland, who was deeply involved in the effort to pressure Ukraine to announce investigations into Mr. Trump's Democratic rivals, 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 a political opponent.