Rep. Justin Amash (I-Mich.) said Monday that he’s considering a White House run against President Trump, a move that could pose a challenge to the president’s campaign for a second term.

Amash, who left the Republican Party last year and is seeking reelection to his Grand Rapids-area House seat as an independent, made the comment in a tweet responding to a statement by Trump on Monday night that as president, his “authority is total.”

“Americans who believe in limited government deserve another option,” the libertarian-leaning congressman tweeted. In a follow-up tweet to a supporter, he added, “Thanks. I’m looking at it closely this week.”

A spokesman for Amash did not respond to a request for comment.

Amash’s pronouncement came as Trump was making sweeping — and incorrect — claims about his presidential authority during Monday’s coronavirus task force briefing.

It also came on a day when Democratic support was coalescing around former vice president Joe Biden, the party’s presumptive nominee. Hours earlier, Sen. Bernie Sanders (I-Vt.) announced that he was endorsing Biden’s presidential bid, in a carefully choreographed show of support aimed at bridging the ideological divisions within the Democratic Party.

The Libertarian Party is planning to nominate a candidate for president on May 25 at its convention in Austin, but no well-known figures have entered the race. Former Rhode Island governor Lincoln Chafee, who joined the party last year, abandoned a bid for the nomination this month. Former Massachusetts governor Bill Weld, the party’s 2016 nominee for vice president, returned to the Republican Party this year to run a protest campaign against Trump. Weld ended his campaign last month.

Amash, a vocal critic of Trump, voted for the president’s impeachment last year and has repeatedly declined to rule out a White House run.

“Is there any better time to have a president who might be not from either party?” he asked reporter Declan Garvey in January.

Libertarian Party leaders have urged Amash to run for the nomination, and while they have faced stiff ideological opposition, former Republican elected officials have won the Libertarian nod every time they’ve tried.