A congressman who quit the Republican Party over his frustration with partisanship and disdain for Donald Trump has launched an exploratory committee to seek the Libertarian Party’s nomination for president.

Justin Amash, who represents Michigan’s third district, left his party last summer over his disdain for the hyper-partisan politics that he said had turned Congress into “little more than a formality.” In a Washington Post column announcing his move, he 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.”

On hearing the news of Mr Amash’s departure, Mr Trump called him “one of the dumbest & most disloyal men in Congress” and a “total loser!”

Mr Amash announced his campaign on Twitter, and sounded confident. “Let’s do this,” he wrote.

“Today, I launched an exploratory committee to seek the @LPNational ’s nomination for president of the United States. Americans are ready for practical approaches based in humility and trust of the people.

“We’re ready for a presidency that will restore respect for our constitution and bring people together. I’m excited and honored to be taking these first steps toward serving Americans of every background as president.”

Mr Amash has been talked about as a potential third-party candidate ever since he left the GOP, though hardly as a sure bet to win the presidency. The reaction to his announcement from other anti-Trump Republicans and conservatives was swift and negative.

Republican strategist John Weaver compared him to the Green Party’s Jill Stein, whom some credit with pulling vital votes away from Hillary Clinton in 2016. George Conway, one of the president’s harshest critics and the husband of White House adviser Kellyanne Conway, said that while he admired Mr Amash’s integrity, “the only real effect Amash could have in this campaign is to enhance Trump’s chances. This is a terrible idea”.