The former governor sat down exclusively with George Stephanopoulos.
Former Republican presidential candidate Chris Christie, in his first interview since leaving the 2024 race last month, is addressing how a hot mic moment partially overshadowed the final moments of his campaign.
"I'll tell you, George, it was a complete mistake," Christie said in an exclusive interview with "Good Morning America" co-anchor George Stephanopoulos that aired on Tuesday.
Minutes before he told a room full of supporters that he was ending his bid for the White House, Christie was heard on the event's livestream telling his New Hampshire state director that former U.N. Ambassador Nikki Haley, one of his rivals, was "gonna get smoked" and was "not up to this."
Christie told Stephanopoulos that it was his son Andrew, who was watching from the Dominican Republic, who called and told him, "Hot mic! Hot mic! Hot mic!"
"It's one of those moments I wish, quite frankly, hadn't happened, just 'cause it was a distraction. But on the other hand, I didn't say anything on the hot mic that I didn't essentially say in the speech that I gave about 10 minutes later," Christie said.
The next day, Haley called him, he said.
"It was a 45-second conversation. She told me, 'I know it's a personal decision to get in a race, and it's a tough decision to get out. I heard everything you said last night, including the hot mic.' And I said, 'Uh-huh.' And she said, 'Well, good luck.' And I said, 'Good luck to you,'" Christie recounted.
"So she didn't ask for an apology, you didn't give one?" Stephanopoulos asked.
"No, there's no apology warranted," Christie said.
In his interview with ABC News, Christie, a former Donald Trump supporter turned vocal critic, explained his decision to suspend his campaign just 13 days ahead of the primary in New Hampshire, where he had devoted all of his time and resources.
"We got to the point the Sunday before I dropped out of the race where we did our last -- our last bit of polling came back. And it was clear to us that we couldn't beat Donald Trump," he said. "To me, once I became convinced I couldn't beat him in New Hampshire, it was time to get out."
In his speech ending his campaign, Christie argued that Haley had been too reluctant to directly attack Trump, whom she has called an agent of chaos but also "the right president at the right time."
But despite Haley deploying more direct attacks against Trump since he defeated her in New Hampshire, Christie said he doesn't envision supporting her down the road -- and risk her later endorsing Trump.
"I made a decision in 2016, the only time in my political career where I endorsed someone purely for political reasons, even though I had some misgivings, and that's when I endorsed Donald Trump," he said. "It was the biggest mistake I've made in my political career, and I'm just not gonna repeat that mistake for anybody."
Christie said it was "hard ... to say" if Haley still has a shot against Trump, but, "It doesn't look like it," given polling showing Trump some 30 points above her in her home state of South Carolina, which will hold the next big primary.
This, despite the fact that, according to Christie, Trump "will be more likely than not a convicted felon when he gets on the stage at the nominating convention in mid-July in Milwaukee."
Looking back, Christie said he feels the entire primary was over the night of the first debate -- last August -- when the field didn't do more to condemn that possibility.
"Because when they ask you, 'Would you still support him if he was a convicted felon?' -- and six of the eight people raise their hands on that stage, what it says to the largest debate audience we were ever gonna have during the primary is, 'His content is normal,'" Christie said.
Only he and former Arkansas Gov. Asa Hutchinson said they wouldn't support Trump if Trump is convicted.
Trump has denied all wrongdoing and pleaded not guilty in his four criminal cases.
"The biggest frustration for me is that we have so many people in our party who complain about Donald Trump [privately], but none of them are willing to do the hard work that needs to be done to rid our party," Christie said at another point in his interview with Stephanopoulos, adding that he feels they're "afraid of him."
When Christie votes in New Jersey's primary in June, he anticipates skipping the presidential portion of his ballot, believing Trump will be the last one standing, he said.
He plans to do the same thing come the general election.
"The one thing I can tell you for sure is I don't know what I'm gonna do in November. But I'm not voting for Donald Trump, under any circumstances," he said.
"Assuming it's the two of them and a handful of third-party candidates," said Stephanopoulos, "isn't any vote that's not for Joe Biden a vote for Donald Trump?"
"In my state, my vote is not gonna matter a lick, OK?" Christie said.
"I don't know who the full field's gonna be yet. And there might be a No Labels candidate," he added, referring to the outside group that is considering a bipartisan "unity" ticket to run against Trump and Biden.
Christie argued a strong Republican could chip away at Trump's support.
Asked directly if No Labels had approached him about joining a ticket, after founding chairman Joe Lieberman said last month he was going to reach out, Christie said he had not -- but didn't rule out the possibility of saying yes.
"Well, what I've said in the past is that I'd have to see a path for anybody -- not just me -- but I think anybody who would accept that would need to see a path to 270, 270 electoral votes," he said.
"If there was ever a time in our lifetime when a third-party candidate could make a difference, I think it's now," he added.
And while he feels Trump is a threat to democracy, he said Biden is "past his sell-by date."
"Joe Biden could sell it better in 2020 than he's able to in 2024, and that is just a product of age," Christie said. "This is not me making some clinical diagnosis. I'm making a political diagnosis that the guy isn't as good as he was four years ago."
Biden has acknowledged concerns about his age but said his record proves his fitness.
Asked the advice he would give to those trying to defeat Trump, Christie said: "Replace Joe Biden. I just think that Joe Biden is probably the only major Democrat who Donald Trump could beat."
Beating Trump has been Christie's mission throughout the 2024 cycle, but he told Stephanopoulos that he couldn't say whether he'll succeed.
"I don't know, George. But it won't be for a lack of trying," he said. "I can guarantee you that."