President Trump fired back at Rep. Justin Amash, R-Mich., on Sunday, a day after Amash became the first Republican congressman to call for Trump's impeachment.

Among other things, Trump called Amash a "total lightweight" and a "loser."

President Trump (Photo: Alex Brandon/AP)

"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 through controversy," Trump tweeted.

Amash, a libertarian-oriented Republican, said Saturday that he had concluded that Trump committed impeachable offenses after reading special counsel Robert Mueller's report on Russian interference in the 2016 presidential election.

Here are my principal conclusions:

1. Attorney General Barr has deliberately misrepresented Mueller’s report.

2. President Trump has engaged in impeachable conduct.

3. Partisanship has eroded our system of checks and balances.

4. Few members of Congress have read the report. — Justin Amash (@justinamash) May 18, 2019

Amash added: "I offer these conclusions only after having read Mueller’s redacted report carefully and completely, having read or watched pertinent statements and testimony, and having discussed this matter with my staff, who thoroughly reviewed materials and provided me with further analysis."

Mueller's report detailed the extensive ways the Russian government sought to influence the 2016 election on Trump's behalf, but found no evidence that any American conspired with the Kremlin in this effort. But Mueller left open the question of whether Trump obstructed justice by trying to interfere with his probe.

In his Sunday tweets slamming Amash, Trump emphasized the lack of an underlying crime when considering the obstruction question.

"If he actually read the biased Mueller Report," Trump wrote, "'composed' by 18 Angry Dems who hated Trump,........he would see that it was nevertheless strong on NO COLLUSION and, ultimately, NO OBSTRUCTION...Anyway, how do you Obstruct when there is no crime and, in fact, the crimes were committed by the other side? Justin is a loser who sadly plays right into our opponents hands!"

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