I was on "Marketplace" the other day talking about the presidential campaign's turn away from national security issues and toward the domestic stuff, and one point I made during the interview (not sure exactly what they actually aired) was that this is likely to change when we move into general election mode. I think there are important differences between the Democratic candidates on foreign policy issues, but they're relatively subtle. By contrast, as Ezra says there's a huge gaping chasm between where the Democrats are and where (assuming Ron Paul doesn't get the nomination) the Republicans are and, as a result, we should expect this subject to come roaring back into view.
Meanwhile, Democrats aren't going to have an easy time of it. George Bush's reputation for incompetence won't automatically transfer to a copartisan, but the press will be very open to stories about Democrats' generic sins of "weakness" on security. Edwards or Clinton will be attacked as flip-floppers; too weak to stand up to their own liberal base, and thus obviously unfit to stand up to Osama bin Laden. Barack Hussein Obama, by contrast, would have left a nuclear-armed Saddam Hussein in power to blackmail America into submission.
Not that these are irrefutable lines of attack by any means, but there's going to have to be a big fight about it. The Republican nominee isn't going to agree to have a lot of fights about who's best suited to accomplishing broadly shared goals.
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