Bill Weld, the maverick former governor of Massachusetts, announced today that he would form an exploratory committee to challenge President Donald Trump for the Republican Party’s 2020 nomination, presenting himself as a dissident voice in a political party that has abandoned its mainstream roots.

Weld, 73, is the first Republican to announce he will run against the president. But Weld is unlikely to pose a major threat to Trump and he is in some ways an incongruous figure to leap into the presidential fray. Weld is a moderate Republican who ran for vice president in 2016 on the Libertarian ticket. His candidacy might be more of an act of protest than a conventional national campaign.

But appearing in New Hampshire, Weld called it a moral duty to stand against “the hard heart, closed mind and clenched fist of nativism and nationalism.”

“I hope to see the Republican Party assume once again the mantle of being the party of Lincoln,” Weld said, according to video posted by the news station WCVB. “It upsets me that our energies as a society are being sapped by the president’s culture of divisiveness of Washington.”

He continued: “We cannot sit passively as our precious democracy slips quietly into darkness.”

Weld had made little secret in recent months of his interest in challenging Trump in 2020, either by running for the Libertarian Party’s nomination or by contesting the Republican presidential primaries. He met repeatedly with Republicans organizing opposition to the president, and earlier this month he was reported to have changed his voter registration back to Republican.

Several other Republicans are contemplating challenges to Trump in the primaries, including Gov. Larry Hogan of Maryland and former Gov. John Kasich of Ohio. Trump’s aides have taken the threat of a primary challenge seriously enough to undertake a close review of the rules for the Republican nominating convention and to begin scrutinizing state party chairs and potential convention delegates for political loyalty.

But Trump and his allies have largely declined to go after potential primary rivals in public, trusting that his solid approval ratings with Republicans will insulate him and declining to issue vocal attacks that could have the effect of elevating a challenger.

Weld, a former federal prosecutor from a prominent Boston family, has spent most of his career as the kind of Republican that used to dominate politics across the Northeast. A fiscal conservative who has long supported gay rights and abortion rights, Weld could have some appeal to moderate Republicans who feel alienated from their party as it continues to swing far to the right.

But partisan Republicans also have ample reason to regard Weld with suspicion. He endorsed Barack Obama for president in 2008 over John McCain, before flipping back to the Republican side in 2012 when his friend and longtime ally, Mitt Romney, was the GOP nominee.

Weld then backed Jeb Bush in the 2016 Republican primaries, before defecting to the Libertarian Party to become the running mate of Gary Johnson, the former governor of New Mexico. The two won a little over 3 percent of the vote.

Weld explained his decision to run that year as a function of his horror over Trump’s candidacy, comparing Trump’s rhetoric about immigration to “the glass crunching on Kristallnacht in the ghettos of Warsaw and Vienna.”

It is no accident that Weld unveiled his tentative plan to run for president in New Hampshire, where there is still a sizable community of Republican centrists and independent voters are permitted to vote in partisan primaries.

Weld has some experience with insurgent presidential primary challenges in New Hampshire. In 1992, as a fresh-faced governor from next door, Weld campaigned in the state to help President George H.W. Bush turn back a challenge from Pat Buchanan, a hard-right nationalist in the mold of Trump. Bush defeated Buchanan, but the conservative commentator’s showing in New Hampshire helped sustain his activist campaign nationally and hobbled the president’s re-election.

A New Hampshire contest between Trump and Weld would effectively reverse the roles from 1992 — with the fire-breathing immigration hawk as president, and the low-key aristocrat as his gadfly challenger.

Cassie Smedile, a spokeswoman for the Republican National Committee, dismissed Weld and any other challengers who might emerge, citing Trump’s popularity with Republicans and his “long list of incredible accomplishments for conservatives and the country.”

“The RNC and the Republican Party are firmly behind the president,” she said. “Any effort to challenge the president’s nomination is bound to go absolutely nowhere.”