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Donald Trump slammed Robert De Niro Monday, following the Oscar-winner’s criticisms of him this weekend, telling Fox News that the actor is “not the brightest bulb on the planet.”

“I like his acting, but in terms of when I watch him doing interviews and various other things, we’re not dealing with Albert Einstein,” Trump told “Fox & Friends” Monday. “He can say what he wants but the fact is that this guy has not revealed his birth certificate, a lot of people agree with me.”

De Niro gave an interview this weekend to NBC’s Brian Williams, where he slammed Trump for his thoughts on the president’s birth certificate.

“I won’t mention names, but certain people in the news in the last couple weeks, just what are they doing? It’s crazy. They’re making statements about people that they don’t even back up,” De Niro said. “Go get the facts before you start saying things about people.”

De Niro later confirmed he was talking about Trump.

"It’s like a big hustle. It’s like being a car salesman. Don’t go out there and say things unless you can back them up. How dare you? That’s awful to do. To just go out and speak and say these terrible things? Unless you just wanna get over and get the job. It’s crazy.”

But Trump defended his stance on Obama, saying the response from the public has been overwhelmingly positive.

“What I do best is China, jobs, OPEC, all of this, that’s what I do best, that’s going to be my strength … [But] recently I did a Tea Party event and we had a tremendous crowd. They love this issue. There are so many people that really want him to provide his birth certificate. Now you have states going out and saying, ‘In order to run for office, you have to be able to provide a birth certificate.’ There’s a big lot of things going on with respect to the birth certificate.”

“Why is he spending millions of dollars to fight this issue, instead of just providing his birth certificate?” Trump added about Obama. “There are so many different elements here and I will say, it’s a very frightening thing for this country.”

De Niro is among a growing number of Hollywood stars who have criticized Trump for his comments, including comedian Jerry Seinfeld.