• Donald Trump dismissed more questions about whether he would release his current medical records.
• Kamala Harris is working to sow doubts about his physical and mental fitness for the presidency.
• Trump would become the oldest person in U.S. history elected president if he prevails in the Nov. 5 election.

Donald Trump on Friday dismissed more questions about whether he would release his current medical records, doubling down on refusing to provide a health update even as Kamala Harris works to sow doubts about his fitness for the presidency.

The 78-year-old Republican nominee, when asked if he will release his health records, suggested that he has already shared enough information about his medical status.

"Yeah, my health records – I've done five exams over the last four years. You've got them all," Trump told a reporter on an airport tarmac after landing in Detroit, Michigan, on Friday afternoon.

Trump then appeared to suggest that he was too busy campaigning against Vice President Harris, the Democratic nominee, to devote time to update his records.

"Obviously, I'm in the middle of a very big and very contentious fight," he said. "We're leading. I've given my health exams."

Trump added that he has "done cognitive tests twice, and I've aced them. Meaning a perfect score."

"I want to see her do a cognitive test because she couldn't ace because she wasn't born smart," he said, before walking away from the press.

The Trump campaign did not respond to CNBC's request for additional comment on Trump's remarks in Michigan.

Trump told CBS News in August that he would "very gladly" release his medical records, but his campaign has not done so.

Harris, who turns 60 on Sunday, released a detailed health report from her White House doctor on Oct. 12. That same day, Trump campaign spokesman Steven Cheung claimed in a statement that the Republican nominee "has voluntarily released" multiple health reports.

Cheung pointed to a three-paragraph letter from Dr. Bruce Aronwald, which was shared last November and related to an exam of Trump that was conducted more than a year ago.

Cheung also referred to two memos penned in July by Republican Rep. Ronny Jackson of Texas, who formerly served as Trump's White House physician. Those memos focused on the injury Trump sustained when he narrowly survived an assassination attempt at a July 13 campaign rally.

Harris, meanwhile, has recently ramped up her health-focused attacks on Trump, who would become the oldest person in U.S. history elected president if he prevails in the Nov. 5 election.

During a rally in North Carolina on Sunday, she put a spotlight on Trump's refusal to release a comprehensive health report, along with his decision not to agree to a second debate.

"It makes you wonder, why does his staff want him to hide away? One must question, one must question, are they afraid that people will see that he is too weak and unstable to lead America? Is that what's going on?" Harris said.

On Friday, she seized on a Politico report that a Trump advisor had told a podcast that the former president backed out of an interview on the show because he was "exhausted."

Trump has also scrapped a handful of other interviews — including one with CNBC — in the final weeks before Election Day.

"If he can't handle the rigors of the campaign trail, is he fit to do the job? I think it's a legitimate question," Harris said at an event in Grand Rapids, Michigan.

Harris has also questioned Trump's mental fitness. In a widely viewed Fox News interview on Wednesday evening, Harris said Trump "is unfit to serve," "unstable" and "dangerous."

She has also mocked Trump over his bizarre town hall event near Philadelphia on Monday night.

After a pair of medical emergencies interrupted the planned question-and-answer session, Trump opted to just listen to music while standing onstage in front of the crowd. That interlude, which lasted 39 minutes, featured Trump swaying to the music while offering few remarks.

Harris' account on X reacted dryly: "Hope he's okay."