MANCHESTER, N.H. (AP) - Republican former New Jersey Gov. Chris Christie kicked off his presidential campaign Tuesday evening, promising to be the only candidate in a crowded GOP primary field willing to directly take on former President Donald Trump.

Christie, who also ran for president in 2016, began his bid under the slogan “Because the truth matters” with a town hall in New Hampshire, which holds the nation's first Republican primary following Iowa's leadoff caucuses. After losing the nomination to Trump seven years ago, the former governor and federal prosecutor went on to become a close off-and-on adviser before breaking with the former president over his refusal to accept the results of the 2020 election.

“Donald Trump made us smaller by dividing us even further and pitting us one against the other,” Christie said, suggesting that the former president was part of a broader political effort to “paint all Republicans with just one brush.”

He added that President Joe Biden “is doing the same thing, just on the other side.”

Christie enters a growing primary field that already includes Trump, Florida Gov. Ron DeSantis, former United Nations Ambassador Nikki Haley and U.S. Sen. Tim Scott of South Carolina. Former Vice President Mike Pence will be formally launching his own campaign in Iowa on Wednesday.

During his time as governor, Christie established a reputation as a fighter with a knack for creating viral moments of confrontation. But he faces an uphill battle to the nomination in a party that remains closely aligned with the former president, despite Trump's reelection loss in 2020 and Republicans' poorer-than-expected showing in the 2022 midterm elections.

Christie has become a fierce Trump critic in recent years and is now casting himself as the only Republican presidential candidate willing to openly pick fights with the former president - while also warning that the party failing to fully confront him will spark a repeat of the 2016 GOP primary, when Trump rolled over a host of alternatives with more political experience who split the support of voters opposing him.

Anti-Trump Republicans are particularly eager to see Christie spar with Trump on a debate stage - if, of course, Trump agrees to participate in primary debates and Christie meets the stringent fundraising criteria set by the Republican National Committee for participation.

JP Marzullo, a former state representative and former vice chairman of the New Hampshire Republican Party, previously backed Trump but is now supporting Christie.

“I think he'll actually unite some of the voters, and he'll get to independents,” Marzullo said of the former governor, adding, “I think it's time for a change.”

Christie's campaign will test the appetite among Republican voters for someone who has expressed support for many of Trump's policies but has criticized the former president's conduct. The former governor has rejected Trump's lies that the 2020 election was stolen and has urged the party to move on or risk future losses.

Other Republicans with similar views, including former Maryland Gov. Larry Hogan and New Hampshire Gov. Chris Sununu, have opted against their own campaigns, expressing concerns that having more candidates in the race will only benefit Trump.

Christie was at one point seen as one of the Republican Party's brightest political stars as the popular Republican governor of a Democratic state. But despite persistent urging from top donors and party officials, he declined to run for president in 2012. By the time he announced in 2016, his reputation had been tarnished by the “Bridgegate” scandal in which aides were accused of wreaking traffic havoc in Fort Lee, New Jersey, in an apparent effort to punish the city's mayor for failing to endorse his reelection bid.

In the packed 2016 GOP primary, Christie portrayed himself as a brash, tough-talking East Coaster who could “tell it like it is” - only to be eclipsed by the brasher Trump.

Christie opting to start his 2024 bid at a New Hampshire town hall recalled his first run at the White House, when he focused on the state, holding dozens of New Hampshire town hall events only to finish sixth in its primary. He dropped out of that race afterward.

Two weeks later, Christie stunned even some former aides when he endorsed Trump, becoming the first sitting governor and former rival to get behind the emerging GOP front-runner. His announcement undercut rival Marco Rubio at a crucial moment - the day after a debate that had been seen as a possible turning point in the race - helping to pave the way for Trump's nomination and eventual win.

“The line of supporting Donald Trump starts behind me,” Christie has said.

The former governor, who has known Trump for nearly 20 years, has had a complicated friendship with the former developer and reality TV star. At times, he was one of Trump's closest advisers: He was on the shortlist to serve as Trump's vice president, oversaw Trump's early White House transition efforts, said he was offered - and turned down - multiple Cabinet positions, and helped Trump prepare for each of his general election debates in 2016 and 2020. (It was during those debate preparations that Christie believes he caught COVID-19, landing him in intensive care.)

But Christie also clashed with Trump at times and has described the former president's refusal to accept his 2020 election loss to Democrat Joe Biden as a breaking point. In appearances and interviews, Christie says he was “incredibly disappointed and disillusioned” by Trump's refusal to concede, which culminated in his followers' violent storming of the Capitol on Jan. 6 in an effort to halt the certification of Biden's win.

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Colvin reported from New York. Associated Press Writer Will Weissert contributed to this story from Washington.