Joe Biden slammed Republican presidential candidate Rudy Giuliani at Wednesday night's debate, saying he is "the most uninformed person on American foreign policy now running for president."

MR. VANDEHEI: Mayor Giuliani, this question comes from Eric Taylor (sp) from California. He wants to know, what is the difference between a Sunni and a Shi'a Muslim?

MR. GIULIANI: The difference is the descendant of Mohammed. The Sunnis believe that Mohammed's -- the caliphate should be selected, and the Shi'ites believe that it should be by descent. And then, of course, there was a slaughter of Shi'ites in the early part of the history of Islam, and it has infected a lot of the history of Islam, which is really very unfortunate.

GIULIANI: I honestly think we might have gotten tougher questions during the Fox interview, but they were substantive questions. During the MSNBC situation, we got some really good questions. But we also got some of the trick questions: Shia and Sunni.

You know, do I know the difference between Shia and Sunni? I felt like I was, you know, defending my doctoral thesis. It happens that I am a student of the history of religion.

HANNITY: Sure.

GIULIANI: So I knew the answer to that.

"I have very, very strong views on religion that come about from having wanted to be a priest when I was younger, having studied theology for four years in college," he said. "It's an area I know really, really well academically.

Chris Cillizza:...Former New York City Mayor Rudy Giuliani looked like he might stumble when asked to explain the difference between Sunni and Shia but wound up getting it exactly right...

Anonymous: You said that Mayor Giuliani aced the Sunni/Shia question. What event in history was he referring to when he said "and then of course there was a slaughter of Shiites in the early part of the history of Islam, and it has infected a lot of the history of Islam, which is really very unfortunate"?

Chris Cillizza: I don't claim to be an expert on the history of the Sunni and Shia. In the coverage I watched following the debate, it appeared as though Giuliani was factually correct about the differences between the two groups. That was all I was referencing. And, from a political standpoint, I think Giuliani dodged a major bullet with that question. I wonder how many of the ten men on that stage last night could have come up with something approximating a right answer on that question.