Nikki Haley swipes at Biden's age, says he's 'not likely' to 'make it' to 86

Republican presidential candidate Nikki Haley has again swiped at President Joe Biden's age after he formally launched his 2024 bid this week and on Thursday the White House shot back.

Haley suggested during an interview with Fox News Wednesday that Biden wouldn't "make it" to the end of a second term were he to be reelected.

"He announced that he's running again in 2024, and I think that we can all be very clear and say with a matter of fact that if you vote for Joe Biden you really are counting on a President Harris, because the idea that he would make it until 86 years old is not something that I think is likely," Haley said.

The Haley campaign continued that criticism on Thursday, tweeting: "A vote for Joe Biden is a vote to make Kamala Harris president."

The former South Carolina governor, who is 51 years old, jumped into the race for the GOP nomination in February. She's pitched herself to voters as much-needed generational change against figures like Biden, 80, and Donald Trump, 76.

Asked for a response Thursday, White House deputy spokesman Andrew Bates told ABC News: "As you know, we don't engage with campaigns. But honestly, I forgot she was running." (Biden's campaign declined to comment.)

Haley's platform includes proposed mandatory mental competency tests for politicians over 75, though she hasn't elaborated on what those tests would look like or entail.

Biden is the oldest sitting president in U.S. history, and if he's successful in the next election would be 82 when sworn in for a second term and 86 by the time that term ended.

Questions about his age have swirled around his reelection announcement. Biden said he took a "hard look" at his age himself when weighing whether to run again and respects Americans doing the same.

"I can't even say, I guess, how old I am. I can't even say the number, it doesn't register with me," Biden told ABC News Chief White House Correspondent Mary Bruce on Wednesday.

"But the only thing I can say is that one of the things that people are going to find out, they're going to see a race and they're going to judge whether or not I have it or don't have it," Biden continued. "I respect them taking a hard look at it, I'd take a hard look at it as well."

Biden's critics jumped on an exchange with he had with kids Thursday when he appeared to forget when asked about the last foreign trip he made -- to Ireland -- as he said it's "hard to keep track" of all his meetings with heads of state.

When previously asked about Haley's proposition of mental competency tests, the White House dismissed the idea, telling ABC's Stephanie Ramos that they've "heard these types of attacks and remarks before."

"If you go back to 2020, they said that the president couldn't do it in 2020 and attacked him there and he beat them," press secretary Karine Jean-Pierre told Ramos in February.

ABC News' Ben Gittleson and Brittany Shepherd contributed to this report.