Who are the "undecided" voters?

I saw a few comments this morning about the composition of the undecided voters who made up the audience of the second Presidential debate. The suggestion was that this group were mostly Obama supporters.  Frank Luntz had a focus group of undecided voters who, it turned out, had mostly supported Obama in the 2008 election.

At first I thought that it was unfair to stack the "undecideds" with Obama supporters. But on second thought, it's entirely reasonable.

If you didn't support Obama in 2008, when he was the non-Bush, the Lighbringer, the Messiah who would slow the rise of the oceans and heal the planet, why would you decide to consider voting for him after four years of misery and gloom, broken promises and record-breaking deficits?

And here's a shocker:  MSNBC's Undecided Voter Panel Swayed by Romney

Frank Luntz is right.  The only undecided voters in this election are the ones who voted for Obama last time and are now either leaning to Romney or are going to stay home.