For Christie, Winning Would Be Great. Beating Trump Would Be a Close Second.

Chris Christie is embarking on a mission that even some of his fiercest allies must squint to see ending in the White House.

But Mr. Christie, the former governor of New Jersey who is now 60 and more than five years removed from holding elected office, has been undeterred, talking up an undertaking that he frames as almost as important as winning the presidency: extricating the Republican Party from the grip of Donald J. Trump.

“You need to think about who’s got the skill to do that and who’s got the guts to do it because it’s not going to end nicely no matter what,” Mr. Christie said in March at the same New Hampshire college where he plans to announce his long-shot bid on Tuesday.

“His end,” he said of the former president, “will not be a calm and quiet conclusion.”

As he enters the race, Mr. Christie has cast himself as the one candidate unafraid to give voice to the frustrations of Republicans who have watched Mr. Trump transform the party and have had enough — either of the ideological direction or the years of compounding electoral losses.

For Mr. Christie — who lent crucial legitimacy to Mr. Trump’s then-celebrity campaign by endorsing him after his own 2016 presidential campaign failed — it is quite the reversal. After helping to fuel Mr. Trump’s rise, Mr. Christie has now set out to author his downfall.

The question is whether there is any market for what he is selling inside a Republican Party with whom Mr. Trump remains overwhelmingly popular.

“Just being like ‘I’m the kamikaze candidate’ — I’m not sure that’s going to play,” said Sean Spicer, the former White House press secretary to Mr. Trump. “For those people who don’t like Trump because of the mean tweets, are they going to like the guy who is mean about Donald Trump?”

Mr. Christie’s flaws as an anti-Trump messenger are manifest. For almost all of Mr. Trump’s four years in the White House, Mr. Christie stood by the president — even catching a near-fatal Covid-19 infection during debate preparations in the fall of 2020 — only breaking with him over his stolen election lie and then the violence of Jan. 6, 2021.

The coming campaign, then, is expected to be something of a redemption tour. Pulled by the allure of the presidency for more than a decade — his decision not to run in 2012 at the peak of his popularity has been the subject of widespread second-guessing — he begins another run unburdened by expectations.

Yes, he is trying to win. He has said he would not run unless he saw a pathway to victory. (“I’m not a paid assassin,” he told Politico.) But he also wants to turn the party from Mr. Trump.

“He won’t like it, but he’s a loser. It’s that simple,” Mr. Christie said of Mr. Trump in an interview last year, shortly after the disappointing midterm election for Republicans.

It’s the kind of quotable line and anti-Trump message that has turned a number of breakaway Republicans into CNN commentators or MSNBC stars and also made them former elected officials.

Central to Mr. Christie’s pitch to disaffected Republicans is his debating skill. The most memorable achievement of his 2016 bid was his takedown of Senator Marco Rubio of Florida.

“You’d better have somebody on that stage who can do to him what I did to Marco,” he said at his March event, regaling the crowd with the story of his bruising confrontation with Mr. Rubio. “Because that’s the only thing that’s going to defeat Donald Trump.”

The first challenge for Mr. Christie, however, won’t be facing Mr. Trump. It will be qualifying for the debate stage. The Republican National Committee’s threshold of 40,000 donors across 20 states could prove especially arduous for a candidate without a small-donor following and whose anti-Trump message seems more likely to lure Democratic contributors than conservative ones.

So far, Mr. Trump, Gov. Ron DeSantis of Florida and Vivek Ramaswamy, a self-funding businessman, have announced that they have hit that threshold. (There is also a 1 percent polling requirement.)

Mr. Spicer, who later hosted a program on Newsmax, the right-wing cable network, noted that Mr. Christie “hasn’t exactly been on conservative media” to maintain a following on the right. “He’s hanging out on ABC,” Mr. Spicer said of the mainstream news network where Mr. Christie has been a paid commentator.

Quick with a quote and savvy about the media — Mr. Christie turned snapping at reporters into a selling point for the G.O.P. base a decade before Mr. DeSantis — he may be banking on the thirst of news organizations for a frontal and colorful fight with Mr. Trump.

After Mr. Trump’s recent town hall on CNN, when he would not say whether he was hoping Ukraine would win the war against Russia, Mr. Christie slashed him as “a puppet of Putin.”

Yet even the relatively small faction of Republicans uneasy about the idea of returning Mr. Trump to power may be leery of Mr. Christie. He not only provided a key early endorsement in 2016, he led his presidential transition, and was passed over for some top jobs while serving as an informal adviser and debate coach through the 2020 election.

“Now you found Jesus?” questioned Rick Wilson, who was an outspoken Republican critic of Mr. Trump before leaving the party entirely. “And now you’re going to be the guy to take the fight to Trump?”

“The credibility factor of Christie as a Trump antagonist is somewhere around zero,” Mr. Wilson said.

Early polling shows that Mr. Christie faces perhaps an even steeper uphill climb than other candidates who are polling with low single-digit support. He received 2 percent in a late May CNN poll, for instance, tied for fifth place with Senator Tim Scott of South Carolina.

But of all the Republican candidates in the poll, the highest share — 60 percent — said Mr. Christie was someone they would not support under any circumstance. That figure was 15 percent for Mr. DeSantis and 16 percent for Mr. Trump.

“You look at it objectively, it’s hard to see a clear lane for Chris Christie, being a Trump opponent and then a Trump acolyte and now a Trump opponent again,” said Neil Newhouse, a Republican pollster who is unaligned in the 2024 race, though some partners at his firm are working with Mr. DeSantis. “There’s not a lot of room in the Republican electorate for that right now.”

Still, in an increasingly crowded field of Republicans — former Vice President Mike Pence and Gov. Doug Burgum of North Dakota are also expected to join the race this week — the Christie team sees opportunity by being the lone candidate interested in breaking so clearly with Mr. Trump.

Other lower-polling candidates have avoided criticizing the former president aggressively, in an attempt not to turn off his supporters. Some, like Nikki Haley, the former United Nations ambassador and governor of South Carolina, have preferred to take shots at Mr. DeSantis, vying to emerge as the leading Trump alternative by tackling him first. But Mr. Christie’s advisers see the path to the nomination running through Mr. Trump.

His supporters have organized a super PAC, Tell It Like It Is, led by a number of veteran Republicans operatives. And Mr. Christie’s decision to begin in New Hampshire is a sign of the state’s central role in his political calculus, where he also based much of his 2016 campaigning, when he held more than 100 town halls. On Tuesday, he is expected to flesh out his vision for the nation in greater detail.

But there are widespread doubts about how far Mr. Christie’s designs go beyond knocking down Mr. Trump. In an editorial on the eve of his kickoff, The Wall Street Journal editorial board wondered if the candidate might have an unintended impact on the race.

“If Mr. Christie isn’t a guided missile aimed at Mr. Trump, is he an unguided one, liable to blow up, say, Florida Gov. Ron DeSantis?” the editorial board wrote.

Sean Hannity, the influential Fox News host, recently questioned whether he even wanted to give Mr. Christie airtime. “You’re only getting in this race because you hate Donald Trump and want to bludgeon Donald Trump,” Mr. Hannity said on air. “I don’t see Chris Christie actually wanting to run and win the nomination. He views it as his role to be the enforcer and to attack Trump.”

Mr. Trump posted the clip on his social media site, Truth Social.

Maggie Haberman contributed reporting.