Potential 2016 presidential contender Donald Trump spoke to ABC's Jonathan Karl Sunday morning and reignited the birther issue that he helped spark back in 2011, questioning the legitimacy of Barack Obama's birth certificate and wondering whether Ted Cruz, who was born in Canada, was eligible to president. "Was there a birth certificate?" Trump asked. "You tell me. Some people say that was not his birth certificate. I'm saying I don't know. Nobody knows. And you don't know, either, Jonathan. You're a smart guy, you don't know, either." "I'm pretty convinced he was born in the United States," Karl said. "Ah!...