ABOARD AIR FORCE ONE — President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE on Wednesday said Democratic presidential candidate Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE is “having a hard time” after former President Carter suggested an age limit on White House hopefuls.

Speaking to reporters aboard Air Force One, Trump said he believed the public should determine whether age is an issues for certain candidates. But he swiped at the former vice president, whose age has been a point of discussion since last week’s Democratic debate.

ADVERTISEMENT

“I met with a man the other day who was 85 years old, the sharpest guy you’ll ever meet,” Trump said. “I’ve dealt with people who were 92, 93, 94, and they were totally sharp.”

“I can’t speak for Biden,” he continued. “I know nothing about it, but he’s given some very strange answers. That I can tell you.”

Carter, who is 94, said at the Carter Center in Atlanta that he felt he would not have been able to serve in the White House past the age of 80 because of the job's demands.

The remark came in response to a question about whether he would consider running for president in 2020, given that he served just one term.

“He said that ... because Biden’s having a hard time, there’s no question about it,” Trump said Wednesday. “But I’m not speaking for Biden.”

Biden, who is 76 and still holds the top spot in most polls of the Democratic primary field, has a history of making gaffes and puzzling comments. But he has come under additional scrutiny following his performance at last week’s debate.

Fellow candidate Julián Castro faced blowback after the former Housing and Urban Development secretary accused Biden of forgetting what he said “two minutes ago,” which some observers viewed as a jab at the former vice president’s age.

Biden was mocked on social media later in the debate when he responded to a question about racial inequality with an at-times rambling answer in which he encouraged parents to put on the “record player” for their children to hear more words and further their education.

Trump, who is 73, has in recent months raised questions about whether Biden has the stamina for the presidency. He has remarked on the former vice president’s mental sharpness at times in comments to reporters, suggesting that his potential opponent in 2020 may have lost step, without offering examples or elaborating.