Before you say, "Polls don't mean anything..." I agree with you. I rarely follow RCP but thought I would take a look. However, this is pretty telling... and definitely a shift in the overall national opinion.
Tonight, will probably also play a critical role in this trending back down, or rising even more. 80 MILLION people watched the 2008 VP debate, and I think we could see the same number this year. Ask most people on the street, and most know Joe "Gaffe Plagued" Biden has a reputation for being... well... Biden.
It's like watching a NASCAR race. You don't necessarily say it - but you all know you watch for the CRASH on the final lap. Tonight, you may get your wish