See, this lady says Barack Obama is "a citizen of Kenya," and wants to know what her Representative plans to do about the fact that a Kenyan has become the president. So Castle says: "Well I don't know what comment that invites. If you're referring to the president, then he is a citizen of the United States."
That is not so much what the crowd wanted to hear! (The Delaware crowd!) So they all boo him. And Castle doesn't really give a shit. "You can boo, but he is a citizen of the United States."
Hah. The Republicans might eventually regret riling up the crazies, so much!