President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE on Thursday celebrated news that Rep. Justin Amash Justin AmashInternal Democratic poll shows tight race in contest to replace Amash Centrist Democrats 'strongly considering' discharge petition on GOP PPP bill On The Trail: How Nancy Pelosi could improbably become president MORE (Mich.), one of his most vocal critics in the House, was leaving the Republican Party, saying it was “great news” for the party.

“Great news for the Republican Party as one of the dumbest & most disloyal men in Congress is 'quitting' the Party. 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!” Trump tweeted.

Great news for the Republican Party as one of the dumbest & most disloyal men in Congress is “quitting” the Party. 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! — Donald J. Trump (@realDonaldTrump) July 4, 2019

Amash has become a virtual pariah since he called for impeachment proceedings against Trump to begin in May, citing "underlying crimes" committed by Trump that were detailed in the Mueller report. He subsequently left the conservative House Freedom Caucus, which he co-founded and is now stocked with staunch White House allies.

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The outspoken libertarian said he was leaving the GOP after he became "disenchanted with party politics and frightened by what I see from it," saying that "the two-party system has evolved into an existential threat to American principles and institutions."

"Today, I am declaring my independence and leaving the Republican Party," Amash wrote in a July 4 op-ed. "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."

Amash has not ruled out a third-party challenge to Trump in the 2020 presidential race. It is also not clear if he will run for reelection in his district, where he faces a challenge from Republican Jim Lowe, who has cast himself as a close ally of the president.