Minneapolis. Summer in Texas is brutal. That's the end of Dallas and Houston, and heat would be a factor for Miami and Phoenix (115 in August, forget about it) too. St. Francisco is nice but a tight fit, same goes for Boston, Washington DC, but if a small city can be made to work, than San Francisco, Washington DC and Boston in that order.
Pittsburgh, Philadelphia, Cincinnati, Detroit, St. Louis, Baltimore are unappealing in all the ways Rust Belt cities are, so axe those.
San Diego, Tampa, Portland, offer water facilities, and Portland would be very interesting. But would people fly around the world to watch the Games and
then be stuck in the hotel with nothing to do. This applies to most of the sites except DC and San Francisco.
Sacramento and Denver really don't belong in the discussion just as the Rust Belt towns.
Which leaves Minneapolis: lots of lakes, cool in the summer, a virgin city, Midwestern but sophisticated ethos, except for damned Michele Bachmann, maybe she can be liquidated before the games? I joke (just in case Homeland Security/ECHELON are watching). An excellent alternative is Seattle. The only problem is rain but that would set up for a great mascot and lots of umbrella and rain slicker sales!