As throngs of convention-goers in Florida and North Carolina contended with hurricane warnings, snarled bus transportation and thick air, many found themselves wishing for the same thing: a dry heat. “I was thinking this morning it’s too bad we’re not in Las Vegas,” Obama’s top adviser, Robert Gibbs, said as he made a beeline from the outdoor security gate toward the air conditioning beckoning from Charlotte, N.C.’s Time Warner Cable Arena last week. “It might be 10,000 degrees, but at least it would be dry.”