Republican congressman Justin Amash’s support for impeachment proceedings against President Trump ratchets up the pressure on House Speaker Nancy Pelosi to call for the same.

Citing “multiple examples of conduct satisfying all the elements of obstruction of justice” uncovered in the Mueller Report, the iconoclastic Michigan lawmaker spared no one in a lengthy Twitter thread on Saturday—calling out Trump, Attorney General William Barr, and other lawmakers he says put partisanship above their own allegiance to the Constitution.

Many were quick to wonder aloud why it was a Republican lawmaker making the case for impeachment rather than top Democrat Pelosi, who has called Trump “unfit” for the presidency but come out against impeachment, saying it’d be too “divisive” for the country.

“Conservative Republican Justin Amash is more principled and forward-leaning on impeachment than Pelosi, Nadler, Neal, and any of the other House Dem leaders right now. Will they wake up?” tweeted Ezra Levin, a former Capitol Hill staffer and co-founder of Indivisible, a movement fighting to “resist the Trump agenda.”

Neither Pelosi nor Senate Minority Leader Chuck Schumer immediately responded to Amash’s argument for impeachment. But at least one Democratic lawmaker appeared to heed his call.

“Come find me in 1628 Longworth. I’ve got an impeachment investigation resolution you’re going to want to cosponsor,” Rep. Rashida Tlaib (D-MI) tweeted at Amash late Saturday.

Reactions from within his own party weren’t quite as encouraging. “It’s sad to see Congressman Amash parroting the Democrats’ talking points on Russia,” RNC Chairwoman Ronna McDaniel said in a statement. “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.”

Pelosi has repeatedly suggested impeachment proceedings would be likely to backfire, suggesting in early March that Trump actually wants to face impeachment to rile up his base. Earlier this week at an event hosted by the Georgetown University Law Center, she said she doesn’t “want to impeach” even though in her opinion, Trump is giving more “grounds for impeachment” with every passing day by ignoring subpoenas issued by House Democrats.

“I believe that we are headed toward an impeachment inquiry,” Democratic Rep. Jamie Raskin, a member of the House Judiciary Committee, told MSNBC earlier Saturday, saying “the anger and frustration is growing.”

In making his case for impeachment, Amash argued that “extreme partisanship” had blinded Congress to the true purpose of impeachment: to “deter misconduct” and get rid of any official who “has engaged in careless, abusive, corrupt, or otherwise dishonorable conduct.”

Trump did not necessarily have to be found guilty of a crime in order to face impeachment, he said.

“Under our Constitution, the president ‘shall be removed from Office on Impeachment for, and Conviction of, Treason, Bribery, or other high Crimes and Misdemeanors.” While 'high Crimes and Misdemeanors' is not defined, the context implies conduct that violates the public trust.”

“Attorney General Barr has deliberately misrepresented Mueller’s report,” Amash said, adding that Barr’s testimony on the report—in which he repeatedly defended Trump’s conduct—made it clear he “intended to mislead the public about Special Counsel Robert Mueller’s analysis and findings.”

Those findings, he argued, did not clear Trump of wrongdoing as Barr has claimed but revealed “that President Trump engaged in specific actions and a pattern of behavior that meet the threshold for impeachment.”

While Mueller did not establish a conspiracy between the Trump campaign and Russia, he did not make any determinations on obstruction of justice, choosing instead to leave that matter up to Congress.

But Amash argues that many members of Congress didn't even bother to read Mueller's report.

“Their minds were made up based on partisan affiliation—and it showed, with representatives and senators from both parties issuing definitive statements on the 448-page report’s conclusions within just hours of its release,” he wrote.

“America’s institutions depend on officials to uphold both the rules and spirit of our constitutional system even when to do so is personally inconvenient or yields a politically unfavorable outcome. Our Constitution is brilliant and awesome; it deserves a government to match it,” he said.

Amash, who identifies as a libertarian, has previously voiced a desire to see a third party challenge Democrats and Republicans in politics and in March said he wouldn’t “rule out” a 2020 run himself.

Meanwhile, his break with the GOP over impeachment could put a big target on his back. A Michigan state lawmaker hinted on Saturday that he might challenge Amash in a primary.

Amash has raised the prospect of Trump facing impeachment before. In early 2017, when then-FBI Director James Comey first accused Trump of asking him to stop an investigation into former National Security Adviser Michael Flynn, Amash said such a move would be grounds for impeachment.

“But everybody gets a fair trial in this country,” he said at the time.