Why NPR And ABC Presidential Polls Contradict

New polls show the presidential race tightening. A Washington Post/ABC News poll has Obama leading by single digits. But an NPR poll shows that McCain is leading by two points.

"We have to take all numbers with a huge grain of salt," Slate.com's chief political correspondent John Dickerson tells Alex Chadwick. He reads between the numbers and discusses whether we can expect a "historic debate moment."