Let the 2020 Republican primary begin? Bill Weld, a former GOP governor of Massachusetts and the 2016 Libertarian VP nominee, announced Friday that he’s created a presidential exploratory committee, the first public step in his planned challenge to Donald Trump.

“Our president is simply too unstable to carry out the duties of the highest executive office in the land,” Weld said in Bedford, New Hampshire. The 73-year-old added: “We have a president who openly praises and encourages despotic and authoritarian leaders abroad while going out of his way seemingly to insult and even humiliate our democratic allies.”

First thing’s first: Weld’s path to the GOP nomination is nearly impossible to imagine. Yes, Trump is incredibly unpopular nationally. Yes, Robert Mueller is investigating nearly everything Trump has ever touched. And, yes, Trump just declared a legally dubious national emergency that flies in the face of pretty much everything small-government conservatives claim to care about. Still, he has a virtual lock on the GOP nomination. An incumbent president has not been denied a nomination for re-election in more than a century (shout out to Chester A. Arthur), and Trump still has broad support from Republican voters and a stranglehold on the party itself. Someone other than Trump winning the GOP nomination would be the biggest anomaly in presidential politics since, well, Trump winning the White House in 2016.

Weld is fiscally conservative but relatively socially liberal, and his support of legal abortion and gay rights would seem to make him a particularly poor fit for today’s GOP. #NeverTrump conservatives would no doubt prefer someone like John Kasich or Mitt Romney in the race. Still, Weld could make things awkward for the GOP if he manages to stick around. The alarm is more difficult to ignore when it’s going off inside your own home. Weld’s conservative criticism may fall on deaf ears within the party, but his moral case against Trump’s authoritarian, kleptocratic, and racist ways will garner plenty of press. It’s easy to imagine Trump responding in embarrassing ways.

If nothing else, Weld would probably make the primary interesting. Consider the twists and turns of his political career: He spent the 1980s as a federal prosecutor before winning his first term as the Republican governor of Massachusetts in 1990. Four years later, he won re-election in the liberal state in a historic rout. Then, while still in office, he ran unsuccessfully for the U.S. Senate against incumbent John Kerry in 1996. Weld then stepped down as governor the following year after President Clinton nominated him as the U.S. ambassador to Mexico—a job he never got to do because Senate Republicans refused him a confirmation hearing, claiming that his support for things like medical marijuana and needle-exchange programs were disqualifying. Weld later moved to New York, where he unsuccessfully ran for governor in 2006. He returned to the public arena again in 2016, this time as the Libertarian vice presidential nominee. Weld, however, spent as much time campaigning against Trump as he did campaigning for his own running mate, former New Mexico Gov. Gary Johnson. Weld went as far as to go on MSNBC in final days of the race to declare, “I’m here vouching for Mrs. Clinton.”

Oh, and back when he was governor, he once ended a news conference touting the cleanup of Boston’s polluted Charles River by jumping into the waterway fully clothed:

Weld’s strategy essentially begins and ends in New Hampshire, where he’ll have to hope voters remember him fondly from his time as governor of Massachusetts. Weld was a lowercase libertarian even before he became an uppercase Libertarian in 2016, which could boost his appeal in the Live Free or Die state. In reality, though, Weld is staging a protest more than he’s running a campaign. He seems just fine with that.

There’s reason to believe such a protest during the primary could harm Trump in the general election. The last two incumbents to face a serious primary challenge both went on to lose re-election: Gerald Ford, who had to fend off Ronald Reagan in 1976; and George H.W. Bush, who beat back Pat Buchanan in 1992. It’s an open question whether those primary challenges wounded the incumbents or simply exposed weaknesses that already existed. In Trump’s case, it’s hard to imagine there are any weaknesses left to expose.