After months of speculation about his plans, Rep. Justin Amash—the Michigan congressman who’s become one of President Trump’s highest-profile conservative critics—is finally moving toward a White House bid.

In a string of tweets Tuesday night, Amash announced he was starting an exploratory committee “to seek” the Libertarian Party’s 2020 presidential nomination.

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

Amash, who has served in the House since 2011, left the Republican Party last year over his support for impeaching Trump. Though he’s won many fans on the Never Trump right for his self-styled stand of conscience, some prominent Trump critics greeted the announcement of his long-rumored presidential ambitions with a mix of frustration and dread.

Former Illinois congressman Joe Walsh, who mounted an ill-fated challenge of Trump in the 2020 GOP primary, said he and his former House colleague were “brothers at the hip” when it comes to the issues—but he won’t be casting a vote for him for president.

“ I think it’s absolute bullshit what he’s doing... This is not the fucking year to do any kind of third party run. ” — Former congressman Joe Walsh

“I think it’s absolute bullshit what he’s doing," Walsh told The Daily Beast on Monday. “... This is not the fucking year to do any kind of third party run.” The only person who can beat Trump, Walsh said, is the Democratic nominee, and he plans to vote for former Vice President Joe Biden in the general election, assuming he officially locks up the nomination.

“So you put country first and you get behind the Democratic nominee,” Walsh said. “You don’t do this little self-interested dance about a third party or a Libertarian run.”

Also quick to castigate Amash on Tuesday night were a pair of advisers for The Lincoln Project, the super PAC organized by prominent Trump-hating Republicans that’s backing Biden. John Weaver, an alum of Sen. John McCain and former Ohio Gov. John Kasich’s presidential runs, tweeted at Amash: “Jesus Christ. Giant ego and little judgement.”

A similar sentiment came from fellow Lincoln Project adviser George Conway, the husband of Trump White House fixture Kellyanne Conway.

“I admired how @justinamash stood up for the rule of law in Trump’s impeachment,” George Conway tweeted. “And needless to say, my views align more closely with Amash’s than Biden’s. But the only real effect Amash could have in this campaign is to enhance Trump’s chances. This is a terrible idea.”

It’s unclear, however, how exactly an Amash run could affect the matchup between Trump and Biden. Some have speculated Amash could play a spoiler role in Michigan, the key battleground state he calls home, denying Trump a crucial 16 electoral votes by peeling off enough disaffected Republicans, independents, or even Democrats. Some Amash backers have privately hoped he’d target a handful of other states in hopes of doing the same. The congressman said last year he had no interest in “playing spoiler.”

If 2016 were an indication, when third party candidates combined for over 4 percent of the vote, Amash could influence the outcome of 2020—though his chances of winning are virtually nonexistent.

A bad sign for Amash was the general lack of interest that hamstrung the few Republican candidates who tried to challenge Trump in the 2020 GOP primary.

Republicans looking for an escape from Trump were given a handful of options during the primary season, though none gave the president a real headache. Former Massachusetts Gov. Bill Weld, Gary Johnson’s 2016 running mate, placed a heavy emphasis on the New Hampshire primary with little success.

Former South Carolina Gov. Mark Sanford also briefly ran against Trump but abandoned the run in November when faced with whether to file for New Hampshire’s GOP primary.

While Never Trump Republican forces managed to become a sizable voice in the media, that megaphone never translated to much electoral or fundraising muscle to help longshot candidates.

Former New Mexico Gov. Gary Johnson, the Libertarian nominee for president in 2012 and 2016, said in an interview before Amash announced that he liked the congressman. But Johnson avoided any talk of an endorsement.

While Johnson also raved about his 2012 running mate, Jim Gray, when discussing the Libertarian nomination, he noted that “Amash has perhaps more credentials.” Gray, who is a retired Orange County Superior Court judge according to a video on his website, is seeking the Libertarian 2020 nomination.

“There’s no question [Amash] has more notoriety than Jim would have,” Johnson told The Daily Beast.

“ Some see Amash’s tenuous political standing back in his western Michigan district as a possible explanation for the timing of his exploratory committee launch. ”

Rumors have swirled about a possible Amash presidential bid since last year, when he formally left the GOP in June after calling for Trump’s impeachment for the conduct outlined in special counsel Robert Mueller’s Russia investigation.

Some see Amash’s tenuous political standing back in his western Michigan district as a possible explanation for the timing of his exploratory committee launch. Amash, running as an independent this year, was facing GOP challenger Peter Meijer—a member of the prominent Michigan retail-chain family backed by the powerful DeVos clan—as well as Democrat Hillary Scholten in a historically GOP district that Democrats see as more competitive.

“One can read into this,” one conservative political operative told The Daily Beast, “that he knew he wasn’t going to win re-election.”