Donald Trump biographer Tim O’Brien said questions of age and mental acuity may be getting to the former president now that he’s running against Vice President Kamala Harris instead of President Joe Biden.

“Biden had become so visibly diminished and the media was more ready to take Biden to task on it on a regular basis,” O’Brien told The Guardian. “That allowed Trump to skate by.”

But with “a different, younger, more acute and vibrant political opponent,” he said, Trump “now often looks ridiculous or unhinged, unfocused or very, very old.”

Trump has made headlines throughout the campaign for his meandering digressions, bizarre rants about sharks and electric boats, and lengthy word-salad non-answers to questions about policy.

For example, Trump last week when asked about making child care more affordable launched into an incoherent aside about tariffs.

Trump is now facing the same questions about his age and mental acuity that Biden did before dropping out ― and O’Brien said Trump knows it, leading to a noticeable change in his speeches.

“The reason he’s now offering these convoluted explanations of his speech patterns in his public appearances is because he’s hyper-aware that people have noted that he’s making even less sense than he used to,” O’Brien told the newspaper. “What we’re seeing now is a reflection of someone who’s very troubled and very desperate.”

He also warned of reading too much into it ― noting Trump free-associates simply because he can get away with it, and because his audience loves it.

“They feel they’re invited into this world through these nonsensical, nonlinear bits of performance art,” said O’Brien, who is senior executive editor of Bloomberg Opinion, author of the 2005 book, “TrumpNation: The Art of Being the Donald,” and former executive editor of HuffPost.