He told the Inside Trump’s Head podcast that one White House staff member said: “I don’t know what that was, but it wasn’t good. Everybody knows it’s a thin line he walks. Is he teetering? Well…”

“This person didn’t complete the sentence,” he added.

“We all become kind of diagnosticians of these old-man presidents. I mean, nobody is going to come out and say, ‘He’s losing it.’ So we all have to make our own judgments about that.

“And I think in this situation, particularly in this situation—in the way that everyone who has a family at some level relates to this—I think the judgment is going to be a devastating one: Trump is off his f—ing rocker.”

Kentucky representative Thomas Massie was among the Republican voices to criticise Trump.

He said on X: “Regardless of how you felt about Rob Reiner, this is inappropriate and disrespectful discourse about a man who was just brutally murdered.”

He added: “I guess my elected GOP colleagues, the VP, and White House staff will just ignore it because they’re afraid? I challenge anyone to defend it.”

The US President doubled down on his comments on Tuesday, maintaining that Reiner was “very bad for our country.”

Trump has always denied any suggestion that he has cognitive or physical health issues.