Rep. Justin Amash, the only Republican member of Congress to have accused President Trump of impeachable acts, stepped down Monday from the conservative House Freedom Caucus — a group he helped found more than four years ago.

Amash’s resignation comes about three weeks after he posted tweets contending that special counsel Robert S. Mueller III documented “impeachable conduct” in his report on Trump’s campaign and administration. In subsequent public statements, he challenged his colleagues of both parties to take action.

His views turned out to be a particular affront to the Freedom Caucus — a group founded in 2015 to push House Republicans in a more purely conservative policy direction. But as Trump rose to dominate the GOP, so, too, has he come to dominate the Freedom Caucus.

After Amash (Mich.) declared Trump’s conduct potentially worthy of impeachment last month, members of the Freedom Caucus took an informal vote disagreeing with him, though they made no formal move to break ties.

House Minority Leader Kevin McCarthy (R-Calif.) said Tuesday that Amash is an outlier among Republicans, citing a number of instances in which the congressman voted with Democrats.

“Justin Amash can determine his own future. But I think, on a philosophical basis, he’s probably in a different place than the majority of all of us,” McCarthy told reporters at the GOP’s weekly news conference.

CNN reporter Haley Byrd first reported Amash’s resignation Monday evening. It was confirmed by an aide, Poppy Nelson.

“I have the highest regard for them, and they’re my close friends,” Amash told Byrd. “I didn’t want to be a further distraction for the group.”

Among its leaders are Reps. Mark Meadows (R-N.C.) and Jim Jordan (R-Ohio), two of Trump’s strongest defenders on Capitol Hill. Both men distanced themselves from Amash’s views last month.

“Justin Amash’s conclusions are poorly informed and fatally flawed and don’t represent the views of any of the Freedom Caucus members that I’m aware of,” Meadows told reporters.

Amash, 39, is serving his fourth term representing a district centered on Grand Rapids. He remains chairman of the House Liberty Caucus, a group with a much lower profile on Capitol Hill that traces its roots to former congressman Ron Paul (R-Tex.).

Amash has not shied away from defending his position in opposition to Trump, holding a lengthy town hall meeting in his district last month where he heard from both critics and supporters.

His criticism of Trump has earned him Republican opposition in next year’s election, though Amash has not announced he will seek another term. He has acknowledged considering instead running for president as a member of the Libertarian Party.