Are there any historical examples of a democratic election "sapping legitimacy" from a growing insurgency movement? This seems to be the key assumption in both Iraq and Afghanistan—that democratic elections will somehow turn public opinion against the insurgents in some undefined way. Is there a theory or empirical support behind this, or is it just something that sounds kind of right?

UPDATE: A-woo-ga! A-woo-ga! Clear the runway! David Brooks to the rescue:

As we saw in El Salvador and as Iraqi insurgents understand, elections suck the oxygen from a rebel army. They refute the claim that violence is the best way to change things. Moreover, they produce democratic leaders who are much better equipped to win an insurgency war.

As Iraqi insurgents understand? Wha--? Point two sounds kind of right, maybe. As for point three, whatever, nothing about a democratic leader makes him or her inherently "better equipped" to wage war. As I recall, the ever-illegitimate Hosni Mubarak has done a plum job of beating Egypt's Islamic insurgency with a stick. Once again: "Dammit, I need quantification!" Also: "Why in the name of Negroponte would you bring up El Salvador?"