Libertarian commentator Hannah Cox thinks that's ridiculous and said as much on Newsmax:
“I think there's a lot of things you could fairly criticize Trump for, but saying that he is declining mentally or isn't all there, I see no indication of that, and that's something that was very heavily discussed during the election. I heard from many people who aren't even diehard Republicans that Trump seemed to have a lot of vivacity for his age.”
Trump takes pride in his continued cognitive ability, Cox said.
“He has a lot of energy in contrast to Joe Biden. He really means to be able to kind of run laps around people who are many years his junior.”
Based on that, Cox thinks Democrats look foolish and desperate.
“I think it's indicative of the fact that Democrats have still not gotten their game together after this crushing loss, and it really from the outside is kind of funny to watch because it seems pretty obvious if I were coming in and calling the shots the things they should be doing and focusing on if they want to get an upper hand back.”
Instead, Democrats are pushing all the wrong buttons, and that could cost them in the mid-terms, Cox said.
“They’re doing absolutely the opposite of all of those (commonsense) things and focusing on really ridiculous niche arguments and just kind of petty things that they want to get into debates over."

While it's not a winning issue for Democrats, it's one that been near to Trump for perhaps as many as seven years ago.
That's when the White House disclosed a cognitive exam taken by Trump during his first term.
Trump often approached the cognitive issue in the run-up to the 2024 election. Going against Joe Biden it was very much a winning issue for Trump.
Trump said he 'aced' the cognitive check-up according to a CNN report in July of 2020, though the network would like to have seen more proof.
"President Donald Trump claimed on Thursday that he recently 'aced' a cognitive test, his latest attempt to dismiss questions about his mental capabilities and attempt to call into question those of presumptive Democratic presidential nominee Joe Biden," CNN wrote.