I think Rich Lowry has the right idea:

Once he's over the momentary embarrassment of his association with Craig, Romney is probably helped by this scandal at the margins. When a party is reeling from scandal after scandal—some of them involving gross sexual misconduct and adultery—the wholesome guy who is loyal to his wife and family is going to look more appealing.

The problem with nominating someone like Giuliani (and to a lesser extent McCain and Thompson) is that it looks like more of the same Washington scandal class (rightly or wrongly). Giuliani’s past just begs for people to draw the easy association to Congressional deviants who are unable to keep their personal conduct under control. McCain and Thompson’s multiple marriages also invite such comparisons, although to a lesser extent than Giuliani. Giuliani’s cries to the press to leave his personal life alone invite more scrutiny from a press who loves to unearth a cover-up, not to mention how precisely they echo a former president’s similar pleas.

Let me make clear that I don’t have any knowledge of personal misdeeds of these men. However, as some candidates have made the “electability” argument against Romney for “flip-flopping”, they miss the beam in their own “electability” eye. If Romney is easily attacked in the general election for insincerity, these men are ripe for attack for scandal. And scandal will be fresher in voters’ minds given its continued permeation in Washington culture.