It's hard to tell exactly what's happening in the run-up to the Democratic primary in Pennsylvania (on April 22). However, several polls show Hillary's advantage over Obama narrowing, and one shows Obama in the lead. Given her big lead in the state as recently as a few weeks ago, a loss in Pennsylvania would be the death blow to Hillary's campaign.

But Obama's sudden surge has coincided with a huge increase in Democratic registrations in Pennsylvania. State officials say there are at least 234,000 new Democratic voters, and they're still counting. This surge is at least partially due to an ambitious voter re-registration effort by the Obama campaign -- which claims that at least 200,000 of the new registrants will back him in the primary:

Another high-stakes voter registration drive just concluded in Pennsylvania, where the deadline to register as a Democrat and participate in the primary was March 24. The Pennsylvania Department of State reports that more than 234,000 voters have either newly registered as Democrats or switched from other parties, and the state hasn't finished counting the new registrations.

"We put together a massive effort," said Hildebrand, saying that the numbers include "over 200k Obama supporters" - an impressive number, and likely more than 10 percent of the total turnout in the primary.

I can't find any indication in these recent polls as to how they are accounting for the influx of new voters. If the larger pool of Obama backers is factored in, it may account for his surging polls. If it isn't, the new round of polls may be underestimating his strength.