The dispute between the acting giant and the curiously coiffed real-estate mogul began over the weekend at the Tribeca Film Festival, when De Niro dismissed Trump's potential run for the White House as "crazy."
According to the Daily Beast, the Oscar-winning actor told NBC News anchor Brian Williams, "I won't mention names, but there are certain people on the news in the last couple of weeks — what they're doing is crazy …They're making statements about people that they don't even back up. Go get the facts before you start saying things about people."
De Niro's reluctance to name-drop aside, Williams pinned down the target of De Niro's ire by asking, "Any of those people have shows on my network on Sunday night?" (Trump's "Celebrity Apprentice" runs on NBC Sundays.) De Niro responded in the affirmative, before characterizing Trump's White House aspirations "a big hustle" and likening Trump himself to "a car salesman."
An irate Trump fired back at De Niro during an interview with "Fox & Friends" Monday morning, calling De Niro's intelligence into question.
"Well he's not the brightest bulb on the planet," Trump opined during the phone interview. "I’ve been watching him over the years, and I like his acting, but you know in terms of when I watch him doing interviews and various other things, we’re not dealing with Albert Einstein."
As for Trump making statements that he can't back up, as De Niro claims? The Donald reasserted his skepticism over President Barack Obama's birthplace, which has been a major plank of Trump's as-yet-undeclared candidacy.
"[De Niro] can say what he wants, but the fact is that this guy has not revealed his birth certificate and a lot of people agree with me," Trump asserted during the "Fox & Friends" interview.
Trump, who recently placed second among potential Republican candidates in a New Hampshire poll, has not been without his detractors since declaring his political aspirations.
MSNBC's Lawrence O'Donnell has also taken his digs at Trump, saying, “the depths of [his] ignorance of the American government would not get him past a citizenship test.”
Watch Trump return fire at De Niro on "Fox & Friends" in the video.