Chris Christie closed out his second presidential campaign much as he began it, with a blistering and personal takedown of Donald J. Trump designed to prompt a reckoning in his party.
Anticipation had been building all day for the remarks from Mr. Christie, a former governor of New Jersey, after news had spilled out hours earlier that he was telling close allies about his decision.
With all three major cable news networks airing the speech live, Mr. Christie used the rare spotlight — something that had largely eluded his campaign — to make an urgent appeal to the better angels of his party. He framed his animosity toward Mr. Trump in sweeping, historical terms and cast himself as the experienced party elder warning of the possible dangers ahead.
“Imagine just for a moment if 9/11 had happened with Donald Trump behind the desk,” Mr. Christie said. “The first thing he would have done was run to the bunker to protect himself. He would have put himself first before this country, and anyone who is unwilling to say that he is unfit to be president of the United States is unfit themselves to be president of the United States.”
Mr. Trump’s campaign responded with a memo from his pollster, John McLaughlin, who said Mr. Christie “was going to be embarrassed” by the results of the Iowa caucuses on Monday and that he was “widely disliked” by voters in New Hampshire, which will hold its primary on Jan. 23. Mr. Christie had focused his campaign on New Hampshire, but struggled to make himself a contender.
Mr. Christie also grappled with his own role in Mr. Trump’s rise, acknowledging that he had capitulated to ambition when he ended his 2016 presidential bid and surprised much of the political establishment at the time by backing Mr. Trump. Mr. Christie described his second campaign as something of a redemption tour.
“I would rather lose by telling the truth than lie in order to win, and I feel no differently today, because this is a fight for the soul of our party and the soul of our country,” he said.
Mr. Christie paced the stage as he spoke and at times appeared emotional, including when he talked about the supporters who had urged him to remain in the race. His voice cracked when he quoted Benjamin Franklin’s warning that Americans had been given “a republic, if you can keep it.”
“Benjamin Franklin’s words were never more relevant in America than they are right now,” Mr. Christie said. “The last time they were this relevant was the Civil War.”
Mr. Christie didn’t spare his rivals in the race, saying in public what he had expressed to others in private: that neither Gov. Ron DeSantis of Florida nor former Gov. Nikki Haley of South Carolina was going hard enough at Mr. Trump.
He said that if Mr. Trump became the nominee, his win would be traceable to the first Republican debate. Mr. Christie was the only candidate on the stage who indicated that he would not support the former president if Mr. Trump were convicted of one of the 91 felony charges he is facing.
“I want you to imagine for a second that Jefferson and Hamilton and Adams and Washington and Franklin were sitting here tonight,” Mr. Christie said. “Do you think they could imagine that the country they risked their lives to create would actually be having a conversation about whether a convicted criminal should be president of the United States?”
But Mr. Christie’s speech is unlikely to move the needle inside the Republican Party. Many of the party’s most towering figures have tried in recent years without success.
In 2016, Mitt Romney used his stature as Republicans’ previous presidential nominee to denounce Mr. Trump as a “fraud” whose promises were “worthless” and who was “playing the American public for suckers.” Mr. Trump won the nomination, and the White House.
After the attack on the Capitol on Jan. 6, 2021, Senator Mitch McConnell, the Republican leader, spoke from the Senate floor to say Mr. Trump’s supporters involved in the attack had been “fed lies” and “provoked by the president.” Mr. Trump was later acquitted in an impeachment trial in the Senate, a decision supported by Mr. McConnell.
Two years ago, Representative Liz Cheney of Wyoming, speaking from the Ronald Reagan Presidential Library, said Mr. Trump was “attempting to unravel the foundations of our constitutional republic” and had “gone to war with the rule of law.”
She was unseated by a Trump-backed primary challenger months later.
Alyce McFadden contributed reporting.