Rep. Justin Amash encouraged others to follow his lead in leaving the Republican Party and becoming an independent. | Bill Pugliano/Getty Images CONGRESS Trump lashes out as Justin Amash says he is leaving the GOP

Justin Amash, the only congressional Republican who has publicly called to impeach President Donald Trump, says he is leaving the GOP, a move that drew a swift rebuke from the president Thursday.

"Today, I am declaring my independence and leaving the Republican Party. No matter your circumstance, I’m asking you to join me in rejecting the partisan loyalties and rhetoric that divide and dehumanize us," the five-term Michigan lawmaker wrote in an opinion piece published in the Washington Post on Thursday morning.


Trump responded hours later on Twitter: "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!"

Amash, a 39-year-old libertarian elected in 2010, faced two primary challenges and Trump's lash on Twitter after saying the president committed impeachable offenses May 18. He also said Attorney General William Barr had “deliberately misrepresented” special counsel Robert Mueller’s report into Russian meddling in the 2016 election and allegations the president sought to obstruct the investigation.

Trump has called Amash "a total lightweight" and "a loser who sadly plays right into our opponents hands!” on social media.

Donald Trump Jr. and Amash feuded on Twitter on June 13 after the president's son teased a campaign appearance for an Amash primary challenger, state legislator Jim Lower, in Michigan's 3rd District.

Amash on June 10 quit the conservative House Freedom Caucus, of which he was a founding member. The group, which has frequently allied with the president, uniformly opposed Amash's impeachment stance. Trump has discussed the idea of a primary challenge to Amash with North Carolina Rep. Mark Meadows, a Freedom Caucus co-founder, and Republican National Committee Chairwoman Ronna McDaniel, a former Michigan GOP leader and Trump ally.

In light of Amash's move to ditch the party, the RNCC will almost certainly support a primary challenger since it only supports Republicans running for office. Amash has told friends and allies in Congress that he didn’t plan on running for president as a libertarian, POLITICO Playbook reported.

In the op-ed, published on the Fourth of July ahead of the president's "Salute to America" on the Mall but which doesn't mention the president by name, Amash stresses his long support for the GOP as the child of Republican-supporting immigrants before criticizing the partisanship of modern-day politics.

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

He adds: "These are consequences of a mind-set among the political class that loyalty to party is more important than serving the American people or protecting our governing institutions. 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."

Amash encouraged others to follow his lead in becoming an independent. "Modern politics is trapped in a partisan death spiral, but there is an escape," he wrote. He had not previously ruled out a run as an independent.

Six hours before his op-ed was published, Amash tweeted a picture of the Declaration of Independence, writing: "Happy Birthday, America!"

On Thursday morning, he tweeted a link to his op-ed, adding: "Today, I'm declaring my independence."

Trump on Thursday traveled by motorcade to Trump National Golf Club in Sterling, Virginia, arriving at 9:07 a.m., according to pool reports.