Jimmy Fallon offered a theory on Donald Trump after an author who interviewed the former president six times said he had “severe memory issues.”

“I’m starting to think he writes his name on buildings just so he can remember where he lives,” the “Tonight Show” host quipped.

He noted that both Trump and President Joe Biden have been accused of having trouble remembering things.

“Which is why they’re starring in the new film, ‘50 First Debates,’” he added, tweaking the name to the 2004 film starring Drew Barrymore as a woman with amnesia.

“Luckily, there’s help out there for Trump,” Fallon went on, introducing a mock ad for a “memory loss pill made specifically for presidents.”

Ramin Setoodeh, who interviewed Trump extensively for his new book, said in media appearances this week that Trump could not remember who he was several months after a lengthy interview in 2021, and also shared several other examples of Trump’s apparent cognitive struggles.

The Trump campaign insisted Trump did not remember Setoodeh because he didn’t make “an impression” on the former president because he’s a “nobody.”

Watch Fallon’s monologue, and the spoof ad, below.