Do the Debates Even Matter?

— -- Sen. John McCain and Sen. Barack Obama head to Mississippi tonight for the first presidential debate of the general election.

For a walk down memory lane (presidential debate edition), check out this video produced by ABCNews.com producer Lindsey Ellerson on memorable debate moments in the election cycles of yore.

And while there were questions on top of questions as to whether or not the debate would go on as scheduled, pundits volleying back and forth over whether it should or shouldn't, ABC News' Polling Director Gary Langer blogs on whether the candidates' debate performances even matter.

Do they?