Rep. Justin Amash (I-MI) formally withdrew from the Republican Party on Monday.

Several days after publishing his scorching Washington Post op-ed announcing his departure from the GOP, Amash sent a letter to House GOP leaders Reps. Kevin McCarthy (R-CA) and Liz Cheney (R-WY) as a “formal notification” of his withdrawal. He also gave up his seat on the House Oversight Committee, his one committee assignment.

“Please accept this letter as formal notification that I am withdrawing my membership in the House Republican Conference, effective immediately, for the reasons outlined in my accompanying op-ed,” Amash wrote.

Today, I sent the attached letter to Republican leaders as formal notification that I am withdrawing my membership in the House Republican Conference and, consistent with House rules, resigning from the Committee on Oversight and Reform. pic.twitter.com/8x8lFUmaGY — Justin Amash (@justinamash) July 8, 2019

According to Politico and the Washington Post, House Republicans were planning on stripping Amash of his committee seat in response to the op-ed anyway.

Amash, who was the only Republican to call for impeachment proceedings before he became an independent, sometimes voted with Oversight Democrats during their investigations into President Donald Trump.

“We owe it to future generations to stand up for our constitutional republic so that Americans may continue to live free for centuries to come,” he said in his op-ed on July 4. “Preserving liberty means telling the Republican Party and the Democratic Party that we’ll no longer let them play their partisan game at our expense.”

Trump responded to the Declaration of Justin-dependence with glee.

“Great news for the Republican Party as one of the dumbest & most disloyal men in Congress is ‘quitting’ the Party,” he tweeted. “No Collusion, No Obstruction! Knew he couldn’t get the nomination to run again in the Great State of Michigan. Already being challenged for his seat. A total loser!”

This story has been updated to include Amash’s formal withdrawal.