I think Obama has waited until the sheer weight of lies and smears hit a critical mass. Now he has complete license (and in fact, encouragement) from the press to hit McCain as hard as he wants to.
This is a good start:
This is, of course, essentially what he did in the primaries. Hillary hit and hit and hit and hit. Then the public decided she was running a crazy negative, slander-filled campaign. The net result was her favorables went down and Obama's went up--even when he counterpunched.
Obama did the same thing over the summer. McCain attacked, and attacked, and attacked, and attacked. Obama didn't seem to retaliate very effectively.
Until the convention.
With a litany of scurrilous McCain attacks having piled up (by the way, that's an ablative absolute, for those of you scoring at home), the rhetorical power of Obama's acceptance speech was greatly magnified in a way that would not have been possible had McCain's attacks been rebutted more fervently.
It feels to me that Obama is repeating this strategy a third time. Yes, it's been muddied by the uncertainty on how to respond to Palin. But the facts are McCain has unloaded his cannons--hurt Obama, but permanently ruined his previously untouchable reputation with the refs. Obama has survived this onslaught and now is the sentimental favorite again--a role that he plays exceptionally well. When he seems wronged, his supporters rally, his fundraising spikes and his volunteer numbers swell.
If the Obama campaign has learned anything over the course of this brutal election cycle, it's that being the frontrunner kind of sucks. The pundits and the comedians turn against you. Your base gets complacent. You are a marked man.
In some ways, being the underdog in the polls (no matter how dubious) is the best thing that could happen to Obama coming into the first debate from a media narrative perspective. I think that David Plouffe, et al. are cool, calm and collected because they geniunely don't think the polls are that important--especially the daily tracking polls. I think they believe in the mathematical reality of the polity and the advantages they have in organization and field work.
As an aside, I think that there is a neat parallel between the 527 and the ground game. Obama is trying to quickly rectify his mistake in defunding the independent 527 organizations. McCain is trying to quickly rectify his lack of ground game deficit with his Palin-energized based. My sense is both of these efforts will come too late for both candidates to close the gap with the other. Both 527s and GOTV efforts require months and months of preparation, and while last minute infusions of energy and capital can help, with fifty days to go, as a great man once said, "time is a luxury you don't have."