I have no doubt that this will hurt McCain. But here's the problem with it: John McCain regrets the Keating 5. Indeed, you could say that his entire subsequent career has been one long apology for it. Repudiating what happened has formed the cornerstone of his current career; in a very real sense, it was the father of McCain-Feingold.
Megan then goes on to explain that the problem with Obama-Ayers is that Obama refuses to apologize for it. In my view, Ayers is one of those radicals that the left so loves because they tried to bring about the revolution that parts of the left want so bad, but most don't have the gumption, thank goodness, to try to manifest it themselves. So, all in all the Keating 5 thing doesn't really make all that much sense, unless of course the American public are a bunch of dolts who know very little about McCain's career.