Donald Trump returned fire at Robert De Niro yesterday on “Fox & Friends,” calling him “not the brightest bulb on the planet.” Trump said by phone, “I like [De Niro’s] acting, but . . . we’re not dealing with Albert Einstein.” De Niro appeared to knock Trump during a Saturday Tribeca Film Festival panel, hosted by NBC’s Brian Williams, when he said, “I won’t mention names, but certain people in the news . . . they’re making statements about people that they don’t even back up.” Although De Niro never used Trump’s name, Williams filled in the blanks that he meant The Donald’s stance on where President Obama was born. Trump responded, “[De Niro] can say what he wants, but the fact is this guy has not revealed his birth certificate.” De Niro’s rep didn’t get back to us.