Florida, Ohio, Pennsylvania and Virginia. Romney needs to win three out of these four states. Florida is easily attainable given he lost it by less than a percentage point to Obama.
So how do we get Romney, a patrician looking man of wealth and privilege, two states with large blue collar voting populations and one state whose northern suburbs lean Democrat?
Christie would help in the Pennsylvania suburbs considering NJ is right next door. Plus Christie is Italian and Irish and a tough guy, so he'd play well in the Philadelphia area.
If HRC has Strickland as VP, then Ohio is going to be tough. Doubling down on the Northeastern Republican aspect might play well in New Hampshire though.
Get those three, and I think Romney is better off targeting Colorado and Nevada (where media is relatively inexpensive and there's more Mormon voters to mobilize in Nevada's case).