MSNBC's Chris Matthews this evening finally got the chance to interview Julian Castro, the Democratic mayor of San Antonio, Texas, whom Matthews insisted had given one of the "greatest" political speeches he ever heard Tuesday night.

It was, of course, a thoroughly softball interview, but it concluded on an odd note, with Matthews delving into his unhealthy obsession with "birtherism" to ask Castro why his home state is so chock full of people who don't believe President Obama is a natural-born citizen [MP3 audio here; video follows page break].

"Tough question for you, why are there so many birthers from Texas?" Matthews demanded. Castro tried to diplomatically answer the question, defending his home state without offending Matthews.

"I don't know that Texas has any more or greater proportion than other places in the United States," Castro began, adding that Texans are "proud of our heritage, of our roots" and so naturally, "sometimes Texas gets knocked a little bit more than it should."

"I guess I would disagree with the premise there," Castro concluded.

"Well, I'll run over the numbers with you some night, Mr. Mayor, you've got a lot of birthers down there. And they are wacky," Matthews countered.