A lawmaker who just announced he’s leaving the Republican party won’t rule out running against Trump in 2020

Rep. Justin Amash of Michigan left the door open to a potential 2020 run against President Donald Trump on Sunday, just days after he announced plans to leave the Republican party.

“I still wouldn’t rule anything like that out,” the five-term congressman said on CNN, responding to a question about whether he would run for president as a third-party candidate. “I have to use my skills, my public influence, where it serves the country best.”

Amash added that as of right now he plans to run for reelection as an independent in his western Michigan district, where Republican candidates have lined up to challenge him. Speculation about a potential 2020 bid has grown louder in recent months, however, alongside his increasingly firm criticism of Trump.

After Special Counsel Robert Mueller in May released a report on his investigation into Russian meddling in the 2016 election and efforts by Trump to thwart it, Amash was the only Republican lawmaker who called for presidential impeachment proceedings.

Amash announced his departure from the Republican party in a Washington Post op-ed published on Independence Day on Thursday, saying he had become disenchanted by the politics of both parties. That came about a month after he cut ties with the House Freedom Caucus, a conservative group he helped establish in 2015.

“Today, I am declaring my independence and leaving the Republican Party,” he wrote. “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. If we continue to take America for granted, we will lose it.”

Amash would change the calculus of President Donald Trump’s bid for reelection in 2020, with the potential to draw votes from his conservative and libertarian supporters. At the same time, the long-shot candidacy could help Trump in some pivotal areas of the country.

In Michigan, where the president defeated Hillary Clinton by less than a quarter percentage point in 2016, an early poll conducted by The Detroit News and WDIV-TV suggested Amash could pull votes from the Democratic nominee next year.

Trump has lambasted Amash repeatedly this year, cheering on his decision to split with the GOP.

“Great news for the Republican Party as one of the dumbest & most disloyal men in Congress is ‘quitting’ the Party,” the president wrote on Twitter on Thursday evening. “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!”

Republican Rep. Will Hurd of Texas, another vocal critic of Trump, said in an NBC interview Sunday that it was “unfortunate” Amash believed his positions and ideas had outgrown the party.

“The Republican Party should be a broad party,” he said. “I shouldn’t be the only African-American Republican in the House of Representatives.”