Chris Christie, a former governor of New Jersey and a Republican, entered the 2024 presidential race on Tuesday, presenting himself as a political fighter and the only contender willing to challenge front-runner Donald Trump.

Being the only Republican candidate up to this point eager to deliver legitimately damaging blows to the former President, Christie offers a unique challenge. He filed his papers with the Federal Election Commission ahead of an evening announcement scheduled in Manchester, New Hampshire.

The 60-year-old native of Newark, who finished sixth in New Hampshire seven years ago, finally embraced Trump and was a major counselor to him before the two broke out over the businessman's refusal to concede loss in the 2020 election.

By claiming last month that the de facto Republican leader was "afraid" of engaging genuine opponents, Christie has already started picking on his old ally.

Trump said he could skip at least one of the first two Republican primary debates because he doesn't want to share the spotlight with candidates who are performing worse in the polls.

"If he really cares about the country -- and I have deep questions about that -- but if he really cares about the country, then he's going to get up there, and he shouldn't be afraid," Christie told conservative radio host Hugh Hewitt. 

Christie has criticized Trump on a variety of topics, calling him "Putin's puppet" over his isolationist stance on Russia's military operation in Ukraine and highlighting the expanding criminal investigations into the troubled tycoon.

A larger field supports Trump, but Christie's participation could disadvantage the front-runner in the polls, according to John Ellis, a former head of Fox News Election Night Decision Desk, who spoke to AFP.

"Because he will attack Trump relentlessly, Christie's campaign will get a ton of coverage in the mainstream press, which may help him do well in New Hampshire," said Ellis.

A day after former Vice President Mike Pence filed the necessary paperwork for his own White House run, Christie announced his campaign, creating the unique situation of two former running partners turning against one another.

Pence once served as Trump's Vice President but claimed to withdraw his support for Trump when he tried to overturn the results of the 2020 election. 

The evangelical Christian plans to officially launch his campaign on Wednesday in the early-voting state of Iowa, joining an already crowded field that includes Florida Governor Ron DeSantis, Trump's main rival.

Along with Doug Burgam, other candidates include former governors Nikki Haley and Asa Hutchinson. Doug Burgam is expected to make an announcement on Wednesday.

Polls consistently show Trump with leads over DeSantis of more than 30 points as the clear early frontrunner. The other candidates aren't breaking double digits.

However, hundreds of felony charges have already been brought against the former President in New York as a result of numerous criminal investigations into his personal and official activities.

Legal observers anticipate that Trump will soon be indicted again for mishandling official documents that were inappropriately stored at his Florida home after being taken without authority from the White House.

Ex-New Jersey Governor Chris Christie

Christie, 60, enters the contest as an apparent underdog, six years after his failed presidential campaign in 2016.

In a Reuters/Ipsos survey conducted May 9-15, only one percent of Republicans indicated that Christie would be their top choice.

Christie has called on the Republican party to get past Trump's unfounded allegations that the 2020 election was rigged, notably in his book "Republican Rescue", Reuters mentioned.

He told Axios in March that even if Trump was the Republican nominee in 2024, he would not vote for him.

A former federal prosecutor, Christie has maintained that he is the only candidate that is able to go head-to-head with Trump, unlike other potential rivals such as Pence and DeSantis, who have mostly avoided confrontation.

His second term as governor was ruined by the so-called Bridgegate scandal, in which two of his assistants were charged with intentionally closing lanes at the George Washington Bridge to New York City to punish a local mayor who refused to back his re-election campaign.

Read more: Ex-New Jersey Governor Chris Christie to launch GOP presidential bid