Former Massachusetts governor Bill Weld officially announced Monday that he will challenge President Trump for the 2020 Republican presidential nomination, after several months of mulling a long-shot bid that would appeal to traditional GOP voters.

Weld made the announcement in an appearance on CNN’s “The Lead With Jake Tapper,” where he described himself as “a Republican who works across the aisle and gets things done.”

“Donald Trump is not an economic conservative. He doesn’t even pretend to be. The country deserves to have some fiscal constraint and conservatism,” he said.

Weld, 73, will face a steep climb against Trump, an incumbent who is deeply popular with Republican voters. Weld last won an election in 1994 and has drifted politically in recent years, even serving as the vice presidential candidate for the Libertarian Party in 2016. But he is now determined to offer the GOP a moderate alternative.

Weld filed official papers with Federal Election Commission on April 1, according to his campaign.

Weld’s entry comes as the Trump political team has touted the president’s standing, both financially and politically. Trump’s reelection campaign raised more than $30 million in the first three months of the year, the campaign said Monday.

“The President is in a vastly stronger position at this point than any previous incumbent president running for reelection, and only continues to build momentum,” Trump campaign manager Brad Parscale said in a statement, unrelated to Weld’s announcement.

Still, if Weld’s campaign did somehow get traction, it could present a headache to the Trump operation, and history has demonstrated the effect of such challenges.

In 1992, President George H.W. Bush faced a troublesome run from the right from commentator Patrick J. Buchanan, who embarrassed the incumbent by winning 37 percent of the vote in the New Hampshire primary and fighting Bush until the national convention. The weakened president lost to Democrat Bill Clinton.

Similarly, President Gerald R. Ford had to fend off a Republican challenge from Ronald Reagan in 1976 before losing in the general election to Democrat Jimmy Carter.

A White House official, who was not authorized to speak publicly, dismissed Weld on Monday as a “relic” and someone who “is a big liberal” on climate change and drug issues. Weld has called climate change a dire threat to the nation and backed the use of medical marijuana for veterans suffering from post-traumatic stress disorder.

“Republican voters don’t want what he’s selling,” the official said. “They want to support the president.”

Weld has previously defended his decision to challenge Trump, saying in February that “Republicans in Washington want to have no election.” His team acknowledges he faces many hurdles but maintains that GOP voters deserve a choice in 2020.

“It is a long shot. But it’s certainly less of a long shot than Donald Trump was when he announced and no one thought he was serious,” Stuart Stevens, Weld’s strategist and adviser since the 1980s, said in an interview. “Tonally, he’s going to run a very different campaign. He’s not mad at the world. He’s not a victim.”

Weld has been a fierce critic of Trump’s nationalism and called it an outgrowth of movements of hate groups in Europe and elsewhere. He told the New Yorker this year that Trump uses a “dog whistle loud and clear” to win support from white supremacists and others.

Stevens, the former chief strategist for Mitt Romney’s 2012 presidential campaign, said he has left his longtime firm, Strategic Partners Media, to work for Weld. His former partner at that firm, Russ Schriefer, is an adviser to Maryland Gov. Larry Hogan (R), who is considering his own presidential bid against Trump.

“I believe competition is good, and Governor Hogan would make a terrific candidate,” Stevens said, when asked about Hogan’s possible candidacy. “A robust Republican primary would be a great thing.”

Hogan, 62, who in November became the second GOP governor in history to win reelection in liberal Maryland, is one of several names that have been floated by Trump critics over the past year. That list also includes former Ohio governor John Kasich, who has conceded that, at least in today’s party, he could not beat Trump in a primary.

Hogan said in an interview last month that he often thinks of his father, the late Maryland congressman Lawrence J. Hogan Sr., as he contemplates his political future. Hogan Sr. was famously the first GOP member of the House Judiciary Committee to call for President Richard M. Nixon’s impeachment in 1974. But he has not yet made a decision.

Leading Trump critics welcomed Weld on Monday but said they are waiting to see how the Republican race unfolds before they make any endorsement.

“It’s great he’s the first one in, breaking the ice,” said William Kristol, a conservative commentator who has encouraged top Republicans to run against Trump. “But there are others looking at it. He’s jumping in a somewhat chilly pool that could get warmer in the coming months if the president is vulnerable.”

Weld’s campaign will put a major emphasis on the New Hampshire primary, aides said, because the state has a history of embracing maverick, more centrist Republicans such as the late Arizona senator John McCain — and they say a victory or strong showing there could catapult Weld’s candidacy.

“New Hampshire likes to surprise,” Stevens said. “The history of New Hampshire is to give candidates a really serious look. Any insurgent campaign has to do well in New Hampshire. History shows us that.”

Jennifer Horn, a former chair of the New Hampshire Republican Party, will serve as Weld’s campaign manager, Stevens said, reflecting the campaign’s strategy. Weld is scheduled to visit New Hampshire on Tuesday for meetings.

In the coming days, Weld’s campaign will circulate a video that plays up the Harvard-trained lawyer’s time as a U.S. attorney appointed by Ronald Reagan. The clip will cast him as someone who “made his bones breaking up a corrupt political machine” in Massachusetts and could do the same for Trump’s Washington, Stevens said.

In a memo released to reporters Monday, Weld’s campaign touted him as a Reagan Republican rather than a moderate, noting that he was once “ranked the most fiscally conservative governor in the country by the Cato Institute and the Wall Street Journal.”

Annie Linskey, Felicia Sonmez and David Weigel contributed to this report.