Trump has 'engaged in impeachable conduct': GOP lawmaker

Rep. Justin Amash has become the first congressional Republican to call for the president's impeachment based on special counsel Robert Mueller's report.

The self-identifying libertarian Republican and frequent Trump critic shared his "principal conclusions" on Saturday, including his assertion that "President Trump has engaged in impeachable conduct" in a Twitter thread on Saturday after reading the full redacted report.

The special counsel did not establish that the Trump campaign or anyone associated with it conspired or coordinated with Russia. He also provided no conclusion on the matter of possible obstruction of justice, choosing instead to leave that decision for Congress.

Amash said that the 448-page report "identifies multiple examples" of the president's conduct "satisfying all the elements of obstruction of justice."

President Trump responded in a tweet Sunday, saying he was "never a fan" of Amash.

"A total lightweight who opposes me and some our great Republican ideas and policies just for the sake of getting his name out there through controversy," he tweeted.

The president went on to call Amash a "loser who sadly plays right into our opponents hands!"

The chairwoman of the Republican National Committee said Amash was "parroting the Democrats' talking points on Russia."

"The only people still fixated on the Russia collusion hoax are political foes of President Trump hoping to defeat him in 2020 by any desperate means possible," said the chairwoman, Ronna McDaniel, said in a statement. "Voters in Amash's district strongly support this President, and would rather their Congressman work to support the President's policies that have brought jobs, increased wages and made life better for Americans."

Democratic House Speaker Nancy Pelosi has stopped short of calling for impeachment but left the door open to the prospect, though Democratic leaders are reluctant to launch a divisive effort that would likely end with the president's acquittal in the GOP-led Senate.

In his lengthy post, Amash stated that partisanship is getting in the way of our system's checks and balances.

"When loyalty to a political party or to an individual trumps loyalty to the Constitution, the Rule of Law -- the foundation of liberty -- crumbles," he said.

Amash has frequently been one of the few Republicans willing to call out Trump when he feels the president has crossed the line.

Amash was one of 13 Republicans to vote with Democrats against Trump's national emergency to fund the border wall. Amash also took a different approach than his fellow Republicans in his questioning of former Trump attorney Michael Cohen. He asked Cohen softer, open questions instead of trying to delegitimize Cohen's testimony and criticize Democrats.

Another one of Amash's primary conclusions from the redacted report was that Attorney General Bill Barr "deliberately misrepresented" Mueller's findings.

"It is clear that Barr intended to mislead the public about Special Counsel Robert Mueller's analysis and findings," Amash wrote.

Barr said he had determined that a case for obstruction was not warranted. In his statement to lawmakers, Barr underscored that the report stated that "while this report does not conclude that the president committed a crime, it also does not exonerate him."

Amash has said as recently as last month that he hasn't ruled out seeking the Libertarian nomination for presidency in 2020.

ABC News' John Parkinson and Will Steakin contributed to this report.