A video clip shows Joe Biden struggling to say "America First," leading to speculation as to whether he is hostile to the phrase or just forgot the words.
Speaking about Trump, Biden stated, "This guy's whole idea of America," before pausing. "America on its own has meant America alone, we're out there by ourselves."
While some claimed Biden couldn't bring himself to use the phrase, it's more likely that he just had another senior moment.
Back in April, Biden managed to remember the phrase "America First," but then went on to embarrass himself by suggesting such a policy approach would prohibit "economic intercourse around the world."
Biden's cognitive functioning has repeatedly been called into question, including last week by White House physician Dr. Ronny Jackson.
"I think that he's old enough now that he's having cognitive difficulties and that just happens. It's part of growing old," said Jackson. "If [Trump] goes head-to-head with Joe Biden cognitively, there just wouldn't be much of an assessment. It will be very one-sided."
Last month, Biden asserted that he is "constantly tested" for cognitive decline.
"Look, all you got to do is watch me and I can hardly wait to compare my cognitive capability to the cognitive capability of the man I'm running against," Biden declared.
Polls show that 38 per cent of American voters think Biden has "some form of dementia," including one in five Democrats.