Donald Trump is doubling down on his jaw-dropping claim that Rob Reiner might still be alive if he’d been nicer about him — branding the acclaimed director a bad influence on the United States.

Asked Monday in the Oval Office about Republicans blasting his earlier remarks following their tragic deaths, Trump vehemently declared he was no fan of Reiner and re-upped his earlier jab, insisting RR was suffering from “Trump Derangement Syndrome.”

Trump went on to claim Reiner made false statements about him — including accusations of being controlled by Russia — making it clear he’s well aware Reiner has long been politically opposed to him and, in Trump’s view, undermining his leadership.

Earlier in the day, Trump politicized the killings on Truth Social, calling Reiner a “tortured and struggling” comedy star and claiming the murders were “reportedly due to the anger he caused others” through what he described as an “incurable affliction with a mind crippling disease” known as Trump Derangement Syndrome.

Nick Reiner — the son of Rob and Michele Reiner, who’s been arrested on suspicion of murdering his parents — stuck out like a sore thumb at Conan O’Brien‘s Christmas party … and he was acting out of place.

Sources at the party, which went down Saturday night at Conan’s, tell TMZ … Nick seemed out of place based on how he was dressed and how he was carrying himself.

We’re told Nick showed up to the very formal party in a hoodie, while everyone else was wearing nice suits and dresses.

Our sources say Nick roamed around in his sweatshirt, didn’t interact with people, kept to himself, and was very reserved … all of which made some folks feel his behavior was odd.

Nick did talk to one person, though … as we first reported, Nick and Rob got into a “very loud argument” at the party, loud enough for many others to overhear. Rob and Michele left the party after the argument, but it’s not clear when Nick left.

The day after the party, Rob and Michele were found in their Brentwood home with their throats slit.

Nick was arrested and booked for murder … he’s in police custody, being held without bail.

Nick’s sister, Romy, found their parents’ bodies and told police Nick had been living with his parents, was “dangerous,” and should be considered a suspect.

Nick Reiner is on suicide watch after being arrested on suspicion of murdering his parents, Rob and Michele Reiner … TMZ has learned.

Law enforcement sources tell TMZ … Nick is on suicide watch and in administrative segregation at Twin Towers Correctional Facility in L.A. … while he’s being held without bail.

As we reported … prior to Rob and Michele’s stabbing, Nick got into a “very loud argument” with his father at Conan O’Brien‘s Christmas party Saturday night. We’re told the shouting match was loud enough for many others to hear, and that Rob and Michele then left the party. We do not know if Nick left with them.

Our family sources told us … Michele had been anguishing to friends over the last few months that she and Rob were at their wits’ end over Nick’s mental illness and alleged substance abuse issues, and did not know what to do with their son Nick … saying, “We’ve tried everything.”