If the economy improves markedly, I wouldn't be surprised to see him gain in MT, ND, AZ, AK, MO, GA, SC, TX and WV.
Pretty much...
A lot rides on his performance in office too. If he does poor in office he might have trouble holding onto states like VA, NC, OH, FL, IN, NV, CO.
A cataclysmic event like 9/11 certainly would make things less difficult, as it would spark nationwide patriotism as seen with Bush in his re-election bid. But no one wishes for cataclysmic events to occur (man-made or nature-caused alike).
Even that depends on his response. Remember Katrina.
