US President Donald Trump unleashed his fury against those who tried to remove him from office, including Republican Senator Mitt Romney, at a prayer breakfast on Thursday, a day after his acquittal by the Senate in his impeachment trial.

Speaking from a stage where he was joined by congressional leaders, including Democratic House Speaker Nancy Pelosi, who led the impeachment charge against him, Trump shattered the usual veneer of bipartisanship at the National Prayer Breakfast in Washington, DC.

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"As everybody knows, my family, our great country and your president have been put through a terrible ordeal by some very dishonest and corrupt people," Trump said at the annual event. His airing of grievances came hours before he was to deliver a full response to the impeachment vote at the White House surrounded by supporters.

"They have done everything possible to destroy us and by so doing very badly hurt our nation," said Trump, who triumphantly held up copies of two newspapers with banner "ACQUITTED" headlines as he took the stage.

His remarks were especially jarring and whiplash-inducing coming after a series of scripture-quoting speeches, including a keynote address by Arthur Brooks, a Harvard professor and president of a conservative think-tank, who had bemoaned a "crisis of contempt and polarisation" in the nation and urged those gathered to "love your enemies".

"I don't know if I agree with you," Trump said as he took the microphone, and then he proceeded to demonstrate it.

"I don't like people who use their faith as justification for doing what they know is wrong," he said in an apparent reference to Utah Senator Mitt Romney, a longtime Trump critic who cited his faith in becoming the only Republican to vote for Trump's removal.

"Nor do I like people who say 'I pray for you' when you know that is not so,'" he said, in a reference to Pelosi, who has offered that message for the president when the two leaders have sparred publicly.

Trump holds up a copy of USA Today's front page showing news of his acquittal in his Senate impeachment trial, as he arrives to address the National Prayer Breakfast [Leah Millis/Reuters]

Pelosi shook her head at various points during Trump's remarks, but did not appear to interact with Trump personally. Earlier she had offered a prayer for the poor and the persecuted.

Trump's comments were a clear sign that the post-impeachment Trump is emboldened like never before as he barrels ahead in his re-election fight with a united Republican Party behind him.

Romney issues scathing criticism

Republican senators voted largely in lockstep to acquit Trump on Wednesday, relying on a multitude of rationales for keeping him in office: he is guilty, but his conduct was not impeachable; his July telephone conversation with Ukraine's president was a "perfect call"; there is an election in 10 months and it is up to voters to determine his fate.

But Romney on Wednesday, ahead of the Senate vote, issued a scathing criticism of the president, saying "corrupting an election to keep one's self in office is perhaps the most abusive and destructive violation of one's oath of office that I can imagine".

Romney voted to convict on the abuse of power charge, and not guilty of the obstruction of Congress charge.

The Republican was the first senator in US history to vote to convict a member of his own party in an impeachment trial.

US senators casting their votes on the second article of impeachment obstruction of Congress during the final votes in the Senate impeachment trial of President Donald Trump [File: Senate TV/Handout via Reuters]

Even with Romney's vote, for Trump, there was one overriding message to draw from his acquittal: even at a time of maximum political peril, it is his Republican Party.

Trump had avoided talk of impeachment in his State of the Union address on Tuesday night, holding his tongue until the Senate had cast its official acquittal vote.

By the next day, he was already moving to use impeachment as a 2020 rallying cry.

Trump tweeted after the Senate vote that he would mark his acquittal with a statement to the nation at noon on Thursday to "discuss our Country's VICTORY on the Impeachment Hoax!" The president's supporters were being invited to join him at the East Room event.

The president and his allies have been on a victory lap since Wednesday, sending giddy tweets needling his accusers and Democrats and celebrating.

Trump also posted a video touting a conspiracy theory that Romney as a "Democrat secret asset" and noted his 2012 loss to Democratic President Barack Obama.

Donald Trump Jr, the president's son, suggested on Twitter that Romney should be expelled from the party.

Other Republicans fall in line

The White House and Trump's allies were also revelling over the continuing chaos in Iowa, where the Democrats' first presidential nominating contest was thrown into disarray by a tabulating mishap, with no official winner declared three days after the caucuses. That deprived any candidate of a clear victory and allowed Trump to paint the Democrats as incompetent.

Trump's tenuous relationship with the Republican establishment has been a consistent theme of his presidency, and he has repeatedly put the party's values to the test. But now, their fates are tied as never before.

Taking their cues from Senate Majority Leader Mitch McConnell, with whom Trump has a respectful, if not particularly close, relationship, Republican senators fell in line to block new witnesses and documents in the trial. The final vote on Wednesday was no different: Only Romney, a longtime Trump critic, voted for removal.

Romney seemed to anticipate retribution, telling Fox News, "I have broad enough shoulders to bear the consequences."