According to the CDC: Adult dogs older than 15 months of age that have previously received a rabies vaccination given no earlier than 3 months of age and that has since expired may be imported immediately following booster vaccination, without the need to wait for 30 days.
Dogs that have never received a rabies vaccination before must be vaccinated at least 30 days prior to arrival in the U.S.
Importation of dogs and cats into the U.S. is regulated by the Center for Disease Control (CDC). According to the CDC, all domestic cats and dogs must show no evidence of disease that can be communicable to humans at the port of entry.
Even if all of your paperwork is in order, if your dog or cat does not look like it is in good health, further examination by a licensed vet (at your expense!) will be necessary before your dog or cat is allowed to re-enter the U.S.!