Barack Obama was as sharp as ever tonight, so when John McCain recited his "Obama doesn't understand..." line from the first debate, Obama retorted with the line of the night.

Obama: Well, you know, Sen. McCain, in the last debate and today, again, suggested that I don't understand. It's true. There are some things I don't understand.

I don't understand how we ended up invading a country that had nothing to do with 9/11, while Osama Bin Laden and Al Qaeda are setting up base camps and safe havens to train terrorists to attack us.

That was Sen. McCain's judgment and it was the wrong judgment.

When Sen. McCain was cheerleading the president to go into Iraq, he suggested it was going to be quick and easy, we'd be greeted as liberators.

That was the wrong judgment, and it's been costly to us.