Robert De Niro joins the ever-expanding lists of celebrities who have taken issue with Donald Trump’s questioning of President Obama’s citizenship.

Trump has made headlines in recent weeks over publicly aligning himself with the “birther” point of view that President Obama is hiding his birth certificate for fear of being exposed as not being born in the U.S.

During a public interview with NBC News' Brian Williams on Saturday night at the Tribeca Film Festival, De Niro took aim at Trump’s stance. The actor said, "I won't mention names, but certain people in the news 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. Go get the facts before you start saying things about people."

When Williams asked if he was referring to a man who has a show "on my network on Sunday night," De Niro confirmed he was referring to Trump.  De Niro continued hammering Trump on his birther beliefs, saying, “Don't go out there and say things unless you can back them up. How dare you? That's awful to do."

In response, Trump said, "I like his acting, but in terms of when I watch him doing interviews and various things, we're not dealing with Albert Einstein."

(Photo: Michael Loccisano/Getty Images)