On a personal level, Paul Ryan's best moment may have come in a show of generous humor toward his opponent.

When Joe Biden labeled Ryan's answer on Iran "a bunch of stuff," moderator Martha Raddatz asked what he meant.

Ryan jumped in. "It's Irish," he said, drawing laughter from Raddatz and Biden.

That kind of off-the-cuff moment can prove key in a debate. It's a nice reminder of some commonality between Biden and Ryan. They're both Irish, after all.