The actor doubled down on his dislike for the ex-Prez during Tuesday's episode ... re-expressing his disdain for DT in a very NSFW way -- going on a cussing tirade on TV.

RDN says he's baffled by the fact that more people aren't taking Trump seriously -- with the businessman leading in several presidential polls heading into November's election.

He went on to say that anyone who doesn't think Trump will do exactly what he says he'll do if he's re-elected is a fool -- and then went in on thinking their lives are going to be made better under Trump, adding ... " excuse my French" before his audio totally cut out.

De Niro's was then cut out of the broadcast ... with the camera panning away so the viewers at home couldn't make out his swear-filled sentiment.

He didn't stop there ... accusing Trump of wanting to do "the worst that he could possibly do to show this country" -- before getting bleeped again. Though, before the camera could move away from De Niro ... it was clear the actor said Trump's slogan should be "F*** America."

This is far from the first time De Niro has spoken out against Trump ... previously saying he wanted to punch the president in the face in 2016. He later blasted Trump again during a speech at the 2018 Tony Awards. He's also wished for bags of crap to be thrown at DT.

Trump eventually hit back at the Oscar winner ... accusing him on Twitter of being "a very Low IQ individual." Safe to say, they're not amigos whatsoever.