ADDED: Was I the first Ted Cruz birther? A year ago, discussing Mitt Romney's remark "No one's ever asked to see my birth certificate," I said:
Romney is saying — in so many words — I'm more truly and fundamentally American than Barack Obama. And the implication is: I want you to think about the ways that Obama hasn't fully embraced American values of freedom, capitalism, etc. etc.
Of course, you don't have to be born in America to have those values. I imagine Ted Cruz has those values, and he was born in Canada. He might make a great Senator from Texas soon, but he can never be President. We don't need to see his birth certificate, because it's no secret. He's not qualified to be President, and it's no disparagement of him to say that. But notably — and pay attention now, because this should help with understanding Romney's joke — no one running against Cruz would make a joke about his being born outside of the United States. Romney's (implicit) joke about Obama works not because of where he was actually born, but because of much more substantive ideas about commitment to foundational American values.
ADDED: Instapundit agrees with me and adds that the press will miss this point and, thinking the joke hurts Romney, will "spread the idea further than Romney could on his own." He also prints email from a reader saying "Why does Ann Althouse assume Ted Cruz is not eligible to be President just because he was born in Calgary? Both of his parents were American at the time of his birth, and his mother was American by birth." I didn't mean to be the first Ted Cruz birther! I agree that if both your parents are American citizens and you are therefore an American citizen at birth, that's good enough for the constitutional requirement.