Clearly part of the Obama team strategy at this point involves daring McCain to take him on in person about William Ayres. Barack himself challenged him last night to "say it to my face", Biden said it too today, and I've heard surrogates on my teevee all day suggesting McCain didn't have the nerve on Tuesday to bring it up when face-to-face.
This could be like Josh says just an effort to get under McCain's skin and make him crazy and even more error-prone, or they may just suspect that the Republican really doesn't want to bring it up in front of anyone but his rabid base, but I'm hoping they know they have a fabulous response ready for when he does bring it up. Better not challenge him like this and not be fully prepared when he takes you up on it next week. This all feels like a brilliant move, but we won't know for sure until all the cards are played out on this one.