As the only Republican in Congress to call for the impeachment of Donald Trump, Justin Amash is facing his own party’s wrath.

In a series of tweets on Saturday, the Michigan congressman said attempts to obstruct justice as outlined in special counsel Robert Mueller’s report on Russian interference in the 2016 election amounted to “impeachable conduct”. He also accused the attorney general, William Barr, of misleading the US public.

In the 48 hours that followed Amash’s intervention, the five-term libertarian was rebuked by the president, dismissed by Republican colleagues and challenged from the right in his district.

Jim Lowe, a Michigan state representative, said on Sunday he would run for Amash’s seat in the Republican primary next year.

“I am a pro-Trump, pro-life, pro-jobs, pro-second amendment, pro-family values Republican,” Lowe said in a statement. “Justin Amash’s tweets yesterday calling for President Trump’s impeachment show how out of touch he is with the truth and how out of touch he is with people he represents.”

Trump said he was “never a fan” of the congressman he called “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 insisted Mueller’s report had found “no collusion” and “no obstruction”. A redacted version of the Mueller report made public last month found no conspiracy between Trump and Russia but laid out extensive evidence of contacts between aides and Russians and detailed 11 instances in which Trump or his campaign may have attempted to obstruct justice.

Mueller did not charge Trump with obstruction, instead punting the issue to Congress. Barr chose to clear Trump of obstruction himself, before Congress had seen the report. The House and Senate have reacted in dramatically partisan fashion. Amash’s tweets therefore broke the mold.

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

“While impeachment should be undertaken only in extraordinary circumstances,” he tweeted, saying that unlike many of his colleague he had read the 448-page report in full, “the risk we face in an environment of extreme partisanship is not that Congress will employ it as a remedy too often but rather that Congress will employ it so rarely that it cannot deter misconduct.”

In a demonstration of the hold Trump maintains over the Republican party, Amash was swiftly and comprehensively rejected by his own colleagues.

Ronna McDaniel, chair of the Republican National Committee, accused him of “parroting the Democrats’ talking points on Russia”. Kevin McCarthy, the House minority leader, questioned if he was truly a Republican.

“What he wants is attention in this process,” McCarthy, a staunch ally of Trump, told Fox News on Sunday. “He’s not a criminal attorney. He’s never met Mueller. He’s never met Barr. And now he’s coming forward with this?

“It’s very disturbing. This is exactly what you would expect from Justin. He never supported the president. And I think he’s just looking for attention.”

Amash, who was elected in the Tea Party election of 2010, has often bucked his party on key legislation. Nonetheless, he has voted with Trump most of the time and is aligned with the conservative House Freedom Caucus.

His comments on impeachment will contribute to debate among Democrats, despite party leaders’ belief that the process would be both politically risky and guaranteed to fail in the Republican-controlled Senate.

On Sunday Adam Schiff, the chair of the House intelligence committee, told CBS: “What may be pushing towards impeachment has less to do with Justin Amash and more to do with the administration engaging in a maximum obstructionism campaign against Congress.”

But the Michigan congresswoman Rashida Tlaib, who has sponsored a resolution to introduce articles of impeachment against Trump, invited Amash to join her.

“You are putting country first, and that is to be commended,” she wrote on Twitter. “We both took an oath to uphold the US constitution.”