I see two moves by Obama himself as being key in helping to cause this shift. First, of course, he directly brought up the subject of Bill's role during the South Carolina debate. But he also did something more subtle, when he made this comment:
I think Ronald Reagan changed the trajectory of America in a way that, you know, Richard Nixon did not and in a way that Bill Clinton did not. He put us on a fundamentally different path because the country was ready for it.
Obama's remarks about Reagan and the Republican party (which, again, he has politely but firmly refused to back down from) contained an allusion to Bill Clinton that looked almost like a throwaway line. I contend that it was very much an intentional provocation aimed at the Clintons -- and it worked exactly as Obama intended.
Both Clintons came out swinging against Obama's comments:
Hillary Clinton: "My leading opponent the other day said that he thought the Republicans had better ideas than Democrats the last 10 to 15 years. That's not the way I remember the last 10 to 15 years." ...
Bill Clinton, speaking of his wife: "Her principal opponent said that since 1992, the Republicans have had all the good ideas. I can't imagine any Democrat seeking the presidency would say they were the party of new ideas for the last 15 years. But it sounded good in Reno, I guess.... So now it turns out you can choose between somebody who thinks our ideas are better or the Republicans had all the good ideas."
Given that Obama's remarks were actually far more benign than the caricatured versions presented by the Clintons, Bill and Hill came off looking petty, extreme, and hypocritical, enforcing a shrill and self-serving political orthodoxy.
Since that final moment of overreach, attack dog Bill has been pretty much kept on a leash. Obama understood the rhythm and intent of his attacker, and found the optimal position and timing to apply a counter-technique. Touché.
I didn’t have the knowledge to make an analogy to Aikido, and I didn’t notice that this was happening with the Reagan reference, but I have come to see Obama as doing this sort of thing. When Big Tent over at http://TalkLeft.com questioned whether Obama could ‘negatively brand’ John McCain, my comment was that Obama had done a good job of ‘negatively branding’ Hillary Clinton, by getting her to do it to herself, and that John McCain seemed susceptible to similar methods.
There has been another instance since then, involving Big Tent. This is when Obama’s campaign (supposedly) suggested to Hillary Clinton that she concede now, before Texas and Ohio. Big Tent claimed this was a big mistake and that Clinton should use it against Obama, saying that he was devaluing the voters of Texans and Ohioans. I reacted immediately: my comment was headlined with an emphatic ‘No!’ and I explained that it was bait, and that if Clinton took the bait then the topic of public discourse would become whether or not Clinton should concede. The commenter just before me pointed out that, also, Clinton would be opening herself to the same charge of devaluing voters (to which she is more vulnerable than Obama is).
Meanwhile, even if Clinton does not take the bait, Obama reinforces whatever urges may be coursing through the brain of Hillary Clinton, leading her towards the action of conceding after Ohio and Texas, should Obama perform sufficiently well in those states.