Donald Trump has reacted angrily to Republican congressman Justin Amash’s announcement that he is leaving the party.The president attacked the Michigan representative, the only Republican in congress to support his impeachment, on Twitter early on Thursday morning.“Great news for the Republican Party as one of the dumbest & most disloyal men in Congress is ‘quitting’ the Party,” Mr Trump wrote.“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!”Mr Amash had only hours earlier quit the GOP, criticising what he described as “dehumanising rhetoric” within the current US political debate.“Today, I am declaring my independence and leaving the Republican Party,” he wrote in a column for The Washington Post.“No matter your circumstance, I’m asking you to join me in rejecting the partisan loyalties and rhetoric that divide and dehumanise 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.”> 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) > > 4 July 2019Although Mr Amash did not mention Mr Trump by name, he has been a long been critical of the president.In May, he clashed with Trump supporters in his constituency during a heated town hall event, claiming they would be “appalled” by details in volume II of the Mueller report into Russian interference in the US election.“I was appalled by it… And we can’t let conduct like that go unchecked,” he told voters in Grand Rapids.He has also claimed he would not rule out challenging Mr Trump as a third party candidate in the 2020 election.Mr Trump has previously called Mr Amash “a total lightweight who opposes me and some of our great Republican ideas and policies” and “a loser who sadly plays right into our opponents’ hands!”Mr Amash, the son of Palestinian and Syrian immigrants, has previously been denounced by the Republican Party following his calls for impeachment.He was first elected to Congress in 2010 and has maintained a strong fiscally conservative agenda and refused to back government spending on healthcare.