Ambinder:

It looks like the deadlier final attack might come not from John McCain, as advertised, but from Barack Obama, with his McCcain-will-cost-you-more blitzkrieg. McCain’s already on extremely weak footing regarding the economy. 

By eliminating McCain’s one economic trump card, that he is a tax cutter and Obama a tax-hiker, Obama’s pounding on those coffin nails.

This is why the "Barack Obama is lying to voters and is a dangerous terrorist pal who can’t be trusted" response is coming from the McCain campaign; their only hope is to erode trust in Obama’s attacks the way Obama eroded trust in mccain’s attacks.