Michigan Rep. Justin Amash said Thursday that he's leaving the Republican Party to become an independent as modern politics remains "trapped in a partisan death spiral."

In an op-ed in The Washington Post that ran on the July 4th holiday, Amash described how he became "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," Amash wrote.

President Donald Trump responded to Amash in a tweet Thursday morning, calling him "one of the dumbest & most disloyal men in Congress" and "a total loser."

Amash was the only GOP member of Congress to come out in favor of impeaching Trump in light of special counsel Robert Mueller's report on Russian interference in the 2016 election.

Amash said in May that Trump "engaged in impeachable conduct" regarding obstruction of justice and accused Attorney General William Barr of distorting the report's conclusions.

The stance drew attacks from the president, who accused the lawmaker of seeking to make headlines.

"Justin is a loser who sadly plays right into our opponents hands!" Trump tweeted.

House Minority Leader Kevin McCarthy, R-Calif., agreed that Amash made his statement because he "wants to have attention."

Mueller's report said the investigation looked into 10 potentially obstructive acts. "While this report does not conclude that the President committed a crime, it also does not exonerate him," the report said, punting that decision to the attorney general. Barr and then-Deputy Attorney General Rod Rosenstein decided not to bring charges against the president.

Amash was one of 13 House Republicans to vote for a resolution against Trump’s emergency declaration on border wall funding, a direct rebuke of the president’s border policies. He has considered running as a Libertarian for president.

Amash did not comment in the Post piece on his presidential plans or whether he'll run for reelection in Michigan's 3rd Congressional District centered around Grand Rapids.

His office did not immediately return requests for comment.

In his op-ed, Amash described how he had been a Republican his entire life, and his parents, both immigrants, were Republicans, too.

"The Republican Party, I believed, stood for limited government, economic freedom and individual liberty – principles that had made the American Dream possible for my family," Amash wrote.

He continued: "Americans have allowed government officials, under assertions of expediency and party unity, to ignore the most basic tenets of our constitutional order: separation of powers, federalism and the rule of law. The result has been the consolidation of political power and the near disintegration of representative democracy."

Amash criticized political parties prioritizing winning elections over all else and congressional leadership that he said forced members to vote on party lines by "dangling chairmanships, committee assignments, bill sponsorships, endorsements and campaign resources."

"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," Amash wrote. "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."

Amash, 39, who was elected to Congress as part of the tea party wave in 2010 and was a state legislator and lawyer before that, didn't mention Trump by name in his opinion piece.

Contributing: Todd Spangler, William Cummings and Nicholas Wu. Follow USA TODAY's Ryan Miller on Twitter @RyanW_Miller