Reuters / Kevin LamarqueJustin Amash—the only Republican who has said publicly that he wants President Trump to face impeachment—is celebrating the Fourth of July in style after announcing that he's quit the GOP.Writing in the Washington Post, Amash made a thinly-veiled attack on Trump in an emotional plea to Americans to reject “the partisan loyalties and rhetoric that divide and dehumanize us.” He went on to say that American politics is trapped in a “partisan death spiral,” and warned : “If we continue to take America for granted, we will lose it.”Amash's decision to quit the party comes after he joined Democratic calls for an impeachment inquiry after the publication of the Mueller Report in April. Since then, he's had to deal with the scorn of his colleagues and has been publicly singled out as a “lightweight” by the president, who said Amash was “a loser who sadly plays right into our opponents hands!”Trump welcomed the news of Amash's exit Thursday, calling him “one of the dumbest and most disloyal men in Congress.” He added: “[Amash] 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!”In his article, Amash quoted extensively from George Washington's farewell address which warned against the dangers of partisanship. Amash wrote that Washington's fears are coming true and that Americans allowed elected officials to toss the constitution aside for the sake of party unity, and that he's become “frightened” by the two-party system in recent years.“Today, I am declaring my independence and leaving the Republican Party,” wrote Amash, summing up his announcement. “No matter your circumstance, I’m asking you to join me in rejecting the partisan loyalties and rhetoric that divide and dehumanize us. I’m asking you to believe that we can do better than this two-party system—and to work toward it.”Amash's departure will fuel speculation that he's hoping to become the nation's leading anti-Trump conservative and seek the Libertarian Party nomination for the 2020 presidential election. He's been evasive on the question before, telling CNN earlier this year that he can't rule out the move because he feels that “someone” has to shake up two-party politics.The move will also throw open the GOP primaries in Michigan's 3rd District, where several Republican candidates have already announced their intention to challenge Amash for his congressional seat.Providing he does try to keep a hold of his seat—which he didn't mention in the article—he’ll now face reelection as an independent.