Obama vs. almost any of the Republicans is Kennedy vs. Nixon redux - if cheating is necessary, national sympathy will go to the telegenic guy. It will be necessary to nominate Romney and hope he can win a couple of Kerry states back by focusing on Obama's inexperience.
That won't help at all. Romney and Rudy cause the Christian right to sit out the election or vote third party. They have never been a particularly captive vote block for the republicans, and will show up for either of these two phonies even less than they showed up for Dole (who had at least fought in WWII). Romney's slickness can't gain as many votes as his liberal history would cost.