Michigan Rep. Justin Amash announced Thursday that he is leaving the Republican Party, saying he is disenchanted and “frightened” by party politics -- a move that was quickly described as "great news" by President Trump.

JUSTIN AMASH GONE FROM HOUSE FREEDOM CAUCUS AFTER SAYING TRUMP'S CONDUCT WAS 'IMPEACHABLE'

Amash, a libertarian and a critic of President Trump, made the announcement in an op-ed for The Washington Post, in which he said he had once run as a Republican due to the GOP’s belief in limited government, economic freedom and individual liberty.

"In recent years, though, I’ve become disenchanted with party politics and frightened by what I see from it,” he said in the op-ed. “The two-party system has evolved into an existential threat to American principles and institutions.”

Trump soon responded, calling Amash's departure "great news" for the GOP and suggesting he quit because he was likely to lose to a primary challenge for his re-election bid.

"Great news for the Republican Party as one of the dumbest & most disloyal men in Congress is 'quitting' the Party," Trump 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!"

Amash is the only House Republican to have called for Trump’s impeachment, and his announcement comes weeks after he resigned from the conservative House Freedom Caucus in June. Amash had said he didn't want to be a "further distraction" for the caucus.

"Some of the president's actions were inherently corrupt," Amash tweeted in May about the findings in Special Counsel Robert Mueller’s Russia report. "Other actions were corrupt -- and therefore impeachable -- because the president took them to serve his own interests."

However, despite his clashes with Trump, Amash did not mention the president in his op-ed Thursday, citing instead “the consolidation of political power and near disintegration of representative democracy.”

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“The parties value winning for its own sake, and at whatever cost. Instead of acting as an independent branch of government and serving as a check on the executive branch, congressional leaders of both parties expect the House and Senate to act in obedience or opposition to the president and their colleagues on a partisan basis,” he wrote.

Amash argues that while Congress was envisioned as a deliberative body to discover new outcomes, instead it has become a formality to legitimize instructions from the president or Congressional leadership.

“With little genuine debate on policy happening in Congress, party leaders distract and divide the public by exploiting wedge issues and waging pointless messaging wars,” he argued. “These strategies fuel mistrust and anger, leading millions of people to take to social media to express contempt for their political opponents, with the media magnifying the most extreme voices.“

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He calls on Americans to preserve liberty by “telling the Republican Party and the Democratic Party that we’ll no longer let them play their partisan game at our expense.”

“No matter your circumstance, I’m asking you to join me in rejecting the partisan loyalties and rhetoric that divide and dehumanize us,” he said.