The McCain campaign is evidently convinced that it can win a debate about Iraq policy, but the basis for their confidence remains elusive. Here's a Democracy Corps analysis of 45 Republican-held but maybe winnable congressional districts:

More importantly, when forced to choose between Obama’s proposal for a responsible troop withdrawal and a shift of resources to the U.S. and McCain’s commitment to stay the course but have most troops out of Iraq by 2013, Democrats win the argument by double-digit margins. Engaging in the Iraq debate allows Democrats to reach out to independents and winnable voters well beyond their electoral support.

Given that this is a somewhat right-of-center set of districts, that's very very bad news for McCain. Under the circumstances, insofar as McCain's heavy recent focus on
Iraq reflects any kind of political strategy, it seems to me to be a kind of confidence game. Republicans are hoping Democrats will fear the issue and shift the conversation elsewhere. Then they'll point to the shifting and say, "see! they're afraid! they know they're wrong!" And I do think that kind of dynamic might change some people's minds. Whether or not it's a good idea to put him on a national ticket, I do think a lot of Democrats running for office could stand to learn from Joe Biden's confidence and recognize that there's nothing to be afraid of.