In a lot of ways, this resembles Sestak's sudden surge in the final weeks of his primary against Specter, after the incumbent had enjoyed wide leads right up until things suddenly changed in that home stretch. But will it last? And what's causing it?
Terry Madonna, a professor at Franklin & Marshall College and a noted analyst on Pennsylvania politics, explained to TPM that the race has become very close for a variety of reasons. Generally speaking, Democratic voters are starting to become more engaged, narrowing the enthusiasm gap. In addition, Sestak's own position has begun to improve among key groups, such as independents and his own party's base.
"Typically, we love to go and say there's one or two things that matter. This matters or that matters. In reality, a lot of things matter," said Madonna. "And it's often three or four little things. We're dealing with a slightly more enthusiastic Democratic electorate, a slightly higher proportion of Democrats for Sestak, and a slightly better situation among independents."
One also has to wonder if this very quirky and memorable ad, in which Sestak says that he has had to work hard to clean up the mess that Republicans have left behind -- comparing it to cleaning up his dog's excrement -- has had an effect:
Okay, I'll admit it. I don't know how much, if any, effect this ad is having on the race. But it really is a great ad, one of the best of the cycle -- summing up a message that practically every other Democrat has struggled to communicate effectively.
If Joe Sestak wins this thing, a whole lot of other Democrats will wish they had his dog -- and her "messes," too.