People are starting to pay attention now and what they see are two Dem candidates doing all they can to undercut the other and working hard to destroy their party's chance of winning. Then they see a GOP guy sitting back and not doing anything idiotic.

You have a choice of forming an initial opinion towards someone who's acting like an idiot or someone who's not acting like an idiot. That puts the advantage in McCain's field.

Now, it's possible that McCain may go ahead and do something irretrievably stupid like campaigning for President or something and blow this opportunity, but as long as the only actions that his team takes is phoning news channels and reminding them that they have to give the GOP guy coverage too, so he's shown wandering around calmly doing his job, he should be able to solidify his lead by the time a battered and bruised Dem nominee tries to drag his or her shattered corpse after him.