Unless there is a major stumble, I cannot find a scenario in which a challenger beats him.
I think you can put CT, PA, ME, RI, and for that matter, DE and NH into the Giuliani column. Ditto for FL. However, I don’t see where a white Catholic Northeasterner would have any overwhelming advantage in the three West Coast states. His strongest appeal is to the blue collar, white Catholic voters, once called Reagan Democrats, who abound in his native Northeast, and Chicago and WI as well, although he is not as alien as a white evangelical Southerner, like George W. Bush or Fred Thompson, is to the heavily secular, lifestyle liberals on the West Coast. I think, however, he can give Hillary or Obama a run for their money in CA, OR, and WA. By forcing the Democrats to spend money in the region (and IL as well, with the large number of white Catholics in Chicagoland) and NY/NJ/CT as well, that will drain Democratic resources that would otherwise be used in light red states like WV, VA, KY, TN, AR, LA, and MO, where Giuliani will suffer some vote loss due to evangelical and conservative indifference or hostility. With Giuliani, the Karl Rove playbook has to be scrapped.