FiveThirtyEight has some evidence to back up williamyard's comment of the day, which predicts that Obama will get a bounce when the debate returns to domestic issues.
Statistically, Obama's advantage on domestic policy is so great that shifting the debate wins him more total support than boosting voters' confidence in his ability to handle foreign policy. In other words, electorally, Samantha Power may be wrong and the Democratic Congressional brain trust circa 2002 may have been on to something.
But that's just in the short run. In the long run, of course, every hit that Obama takes for staking out an alternative foreign policy is a long-term investment in the Democrats' future--and the country's.