I'm basically agnostic on whether Democrats should welcome a national security debate this fall. If they weren't such a bunch of fools and knaves, a rollicking, high-intensity discussion over George W. Bush's expensively failing war, bin Laden's surprisingly successful game of hide-and-seek, and the unpreparedness for disaster that Katrina exposed should be a welcome additive to the GOP's anxieties. But the Democrats often are a bunch of fools and knaves, so who knows how it'll wash out.
What they really do need to stop doing is complaining every time the GOP brings up national security. Every time Republicans bring up security in a pointed fashion, Democrats commence whining about "politicizing" terror. Terror, however, is political, just as health care, jobs, and unemployment numbers are. When Democrats appear reluctant to even discuss the issue, voters conclude, rightly, that they either don't know what they think, don't know what they'd do, or are too scared to verbalize their agenda (a dynamic the Republican Party suffers from on domestic policy). I'm not a consultant and I'm not a foreign policy expert, so I'll let sharper minds than my own puzzle out how to speak about this stuff, but it doesn't take a genius to realize that refusing to address it isn't going to cut your opponent's advantage very much. In any case, Iraq is important. Terror is important. Foreign policy is important. And Democrats want to control the government. Discussing these issues during the election isn't out of bounds, it's a prerequisite.