Michigan Rep. Justin Amash, the only republican in Congress to accuse President Donald Trump of impeachable conduct, is leaving the Republican Party.

In an opinion article for the Washington Post published early Thursday, Amash said modern politics had become “trapped in a partisan death spiral.”

“Today, I am declaring my independence and leaving the Republican Party,” Amash wrote. “No matter your circumstance, I’m asking you to join me in rejecting the partisan loyalties and rhetoric that divide and dehumanize us. I’m asking you to believe that we can do better than this two-party system — and to work toward it. If we continue to take America for granted, we will lose it.”

In June, Amash split from the House Freedom Caucus, a group of conservative lawmakers which he helped found in 2015. Three weeks before leaving the group, Amash posted a series of tweets concluding that Trump had “engaged in impeachable conduct.”