Oh, wait — is Bill Weld a Republican again? Gary Johnson’s running mate on 2016’s Libertarian ticket announced this morning in New Hampshire that he will launch an exploratory committee as the first step to challenging Donald Trump in a 2020 primary. In doing so, Weld sacrifices quite a bit — his potential opportunity to beat Trump in the general election at the top of a Libertarian ticket.

Did I write that with a straight face? You’ll never know.

Former Massachusetts Gov. William F. Weld is launching a presidential exploratory committee to challenge President Trump in the Republican primaries, saying the country is “in grave peril” and he “cannot sit quietly on the sidelines any longer.”

Weld becomes the first Republican to officially announce he is exploring a run against Trump, and sets up a potential match-up in the first-in-the-nation New Hampshire presidential primary and in other states.

In prepared remarks at the “Politics & Eggs” breakfast in Bedford, N. H., Weld delivered a blistering critique of Trump, saying “we have a president whose priorities are skewed toward promotion of himself rather than toward the good of the country.”

“To compound matters, our President is simply too unstable to carry out the duties of the highest executive office — which include the specific duty to take care that the laws be faithfully executed — in a competent and professional matter,” Weld said in his prepared remarks. “He is simply in the wrong place.”

Weld thus becomes the first significant candidate to open up a primary challenge to Trump. Even for someone who hadn’t bailed out of the GOP to run on another ticket, the task would be Sisyphean. Already the RNC has married itself to the Trump campaign in a manner unprecedented in modern American presidential elections. (Okay, okay, almost unprecedented.) At least one RNC member wants to prevent states from holding primary contests at all. Even a sterling, Reaganesque conservative with impeccable loyalty to the GOP would find a 2020 primary challenge a daunting task.

And as Michael Graham reminds usBill Weld ain’t that guy:

If you’re a 2020 GOP primary voter who’s been holding out for a pro-abortion, pro-amnesty liberal who endorsed Barack Obama, praised Hillary Clinton and compared Donald Trump to the Nazis — Bill Weld’s your man!

And if you’re Donald Trump, concerned that a primary challenge could cripple your re-election bid the same way it did for George H. W. Bush or Jimmy Carter, former Governor Weld really is your man.

He’s the ideal candidate for Trump to run against.

Maybe Weld should have entered the 2020 Democratic primaries instead. In this morning’s meeting, Weld expressed dismay over the Democrats’ shift to socialism. He might be a better fit there as one of the lone moderates, plus that would give Weld the hat trick for party affiliations over the last four years.

MSNBC’s Morning Joe broke the news, but they seemed rather subdued about it. John Heilemann probably hits the nose on the head by assessing Weld’s impact as mostly just “the first crack in the dam.” His move could precipitate a challenge from John Kasich, or another Republican with more influence in the GOP. Even that seems pretty unlikely. It would have to be a candidate with his own money, and Michael Bloomberg stopped being a Republican years ago. It’s tough to tell without a scorecard these days, though.