Don't confuse travel with seizure. Your cash, your car, your clothes and anything else you own are subject to seizure anywhere in the U.S. if the DEA (or many other agencies) believe that they have the correct legal evidence. So, for example, if you are legally carrying that same cash from your house in the U.S. to your bank in the U.S., it is still subject to seizure. In fact, if you deposit the cash in the bank it is still subject to seizure.