Sean's an idiot, so it isn't surprising that he'd go in for one of the easiest to debunk (and hardest to believe) conspiracy theories going: the birthers. If you're blissfully unaware, birthers are people who believe all or part of a conspiracy theory that has Barack Obama's mom and/or dad concocting a complicated scheme to make it appear in 1961 that Obama was born in Hawaii, when he really wasn't. Somehow, presenting his "long form" birth certificate, not the shorter certificate of live birth will prove that Obama was really born in Kenya, Indonesia, Canada, on an airplane, or paddling around in a boat in the Pacific Ocean (I'm not kidding).
As the conspiracy got loopier, some of its adherants broke away from it, and now claim that all of that is irrelevant. They say that since Barack Obama Sr. was born in a different country, Jr. is ipso facto not a natural born citizen. Which is preposterous, and would have ruled out other previous presidents as well.
If you want to find a debunking of every goofy birther theory, check out Obama Conspiracy Theories. They're all disproven there. Every. Last. One of them. But even if they weren't, please birthers, explain to me why Mrs. Obama would go to such an effort to fake his birthplace in 1961? Did a fortune teller tell her that one day he'd be president? Because no way she ever guessed that herself.