Let’s cherish these moments while we can.

A week ago today, Obama had a three-percentage point lead and the candidates were even among unaffiliated voters. Today, McCain leads 52% to 37% among unaffiliateds.

McCain is currently viewed favorably by 55% of the nation’s voters, Obama by 51%. That is the lowest rating for Obama since he wrapped up the nomination. Obama is viewed favorably by 83% of Democrats, 22% of Republicans, and 47% of unaffiliated voters. For McCain, the numbers are 87% favorable among Republicans, 26% among Democrats, and 61% among unaffiliated voters…

Forty-six percent (46%) of voters trust McCain more than Obama on energy issues while Obama is trusted more by 42%. Two months ago, Obama had a four point edge on the energy issue (Premium Members can review Crosstabs and Trends).

McCain got out in front of him on drilling and now Obama’s playing catch-up, so the numbers on energy are easily explained. But what about that amazing sudden shift among unaffiliateds? Barnett floats a self-sabotage theory, that the Berlin speech was so underwhelming and anticlimactic as to spark an “emperor’s new clothes” backlash among centrists. That’s wonderful if true, since his alleged rhetorical brilliance is the miracle most frequently cited as evidence of the Messiah’s political divinity, but I don’t buy it. For one thing, it doesn’t jibe with the fact that 55% thought the speech was good or excellent and only 18% thought it was poor; for another thing, the Berlin speech was already a few days old last week when McCain and Obama were dead even among affiliateds. A delayed reaction this pronounced seems unlikely.

It has to be the ads. Like Barnett says, the election is essentially Obama versus Not Obama. It’s hard to pump Not Obama up but not that hard to deflate Obama, especially if the lion’s share of unaffiliateds are centrist conservatives disaffected with the GOP and taking a hard look at the Democrat. For more on that, see Nate Silver’s op-ed today about the electorate’s leftward shift, producing a “median voter” this year who’s more receptive than usual to a true-blue liberal but held in place for the time being by the appeal of McCain’s own centrist maverick-iness. The strategy behind the ads, I take it, is first to demystify Obama by making him faintly ridiculous and then (hopefully) to take David Freddoso’s advice and frame him as a politics-as-usual machine Democrat considerably further left than even that new left-ish median voter. (If you’re wondering how Obama plans to counter, guess.) Makes sense, except … a 15-point swing, from dead even to 52/37, thanks to nothing more than a couple of goofs comparing him to Paris Hilton and Charlton Heston in “The Ten Commandments”? I just don’t buy it. Maybe that dishonest “troops” ad had more effect than anyone thought.

As always, alternate theories are welcome. Exit question data: The same Rasmussen poll puts the electoral college at Obama 273, McCain 227. Gulp.

Update: Headlines comments imported.