Donald Trump on Sunday dismissed as "a total lightweight" the Republican lawmaker who a day earlier became the first member of the party to call publicly for the US president's impeachment.
Michigan Representative Justin Amash -- a staunch libertarian on the right of the party -- declared that any other person would have been prosecuted over Trump's multiple attempts to thwart Special Counsel Robert Mueller's report into Russian election interference.
"Never a fan of @justinamash, a total lightweight who opposes me and some of our great Republican ideas and policies just for the sake of getting his name out there," Trump tweeted.
He said that if the Michigan lawmaker had "actually read the biased Mueller Report... he would see that it was nevertheless strong on NO COLLUSION and, ultimately, NO OBSTRUCTION..."
Trump called Amash "a loser who sadly plays right into our opponents hands!"
Amash, who has broken with his party before, had laid out his case in a series of tweets.
He said Mueller had identified "multiple examples of conduct satisfying all the elements of obstruction of justice."
"Undoubtedly," Amash added, "any person who is not the president of the United States would be indicted based on such evidence."
Since Mueller issued his voluminous report, Trump has repeatedly attacked its authors as partisans even while insisting it exonerates him of allegations of collusion with Russia or obstruction of justice.
But Democrats note that the report lists around 140 contacts between Trump's inner circle and various Russians and that it exhaustively details evidence of at least 10 cases where Trump appeared to be interfering with the probe.
Amash has often been a lone voice in his party, and so his stance carried less impact than if it had come from a party mainstay.
A much higher-profile Republican, Senator Mitt Romney, spoke out on Sunday against impeachment even while praising Amash.
"I respect him," the Republicans' 2012 presidential nominee and occasional fierce Trump critic, told "Fox News Sunday" of Amash.
"I think it's a courageous statement. But I believe to make a case for obstruction of justice, you just don't have the elements."
Democrats have been divided on impeachment but support appears to be growing with the Trump administration resisting numerous congressional requests for witnesses or information.
House Speaker Nancy Pelosi has cautioned against moving too quickly, noting that the Republican-controlled Senate would likely acquit the president should the House of Representatives impeach him.
