Amanda muses on McCain's criticism of Obama's being "too cool and popular." I'm in the midst of Rick Perlstein's excellent Nixonland, and McCain's approach here is exactly along the lines of Nixon's politics of resentment.
Nixon's motivating insight (or instinct) was that, by dint of the nature of popularity ("popular" only makes sense as a relative term; if everyone were equally popular than nobody would be), vastly more people have necessarily experienced feeling left out and looked down upon by the popular than have experienced actually being popular. And so rather than participating in a popularity contest that you are doomed to lose, you can instead attack the contest itself and get people to identify with your unpopularity.
I don't know if this can work for McCain, who I believe has always relied on genuine popularity, especially among the press. But it is far from unprecedented.