Nothing that John McCain has thrown at the wall has stuck. Polls show that independents trust Barack Obama more on the economy and more on handling Iraq. The one survey in which McCain still outscores Obama is on the question of dealing with terror; and he's not up by much, but it's all he has.
I think that's why they've made Ayers their point of attack, and I think there is more to come.
In the final two weeks of the campaign, I expect McCain's closing argument to focus on one question: "If America is attacked again, whom do you want in the White House?" The choices will be the brave POW vs. the guy who hangs out with William Ayers. Expect plenty of 9/11 imagery and "reports" of terrorists plotting an attack to disrupt the election.
This is also one area where Bush can help McCain via the power of the presidency. In the final week before the election, it wouldn't surprise me to see the terror alert status raised and machine gun toting troops back in our airports.
Winning votes with fear is what they do best. Expect it. Be ready for it.