I think we can see where McCain is putting all of his chips now, as the thrust of his campaign is going to be on why Obama hates the troops- literally. As I noted before, this is a line of attack which is beneath contempt, but unfortunately one that will ultimately work for McCain. The reason for why this is going to work is not because the press will support the claims, but because they will breathlessly talk about it.
Furthermore, the focus for this story is not going to be on how McCain is behaving dishonorably, but on Obama. In the 'he said/he said' way that the press reports on the campaign- the debate will be framed as "McCain says that Obama hates the troops, but Obama says that isn't true". With this framing, I think it is easy to see just how it benefits McCain. Case in point.
Ultimately, however, what makes this so frustrating is that the Democrats don't fight on these terms- there are plenty of issues that Obama could connect McCain to and in a way that generates endless debate which paints McCain in an unfavorable light. I think a great line of attack on McCain would be to say that he is in league with oil companies to maximize their profits. Why? Well, you have his recent reversal on coastal oil drilling, his support for the gas-tax holiday (which would be framed as a give away to the oil companies), the public perception that Republicans put corporations first, the fact that Americans are increasingly angry with the oil companies and the added bonus of linking McCain to an industry that Bush and Cheney were heavily involved in.