Please explain to the poster how to re-enter the United States if he/she must leave the cruise and fly back for any reason.
Any TA worth his or her salt will advise a Client to obtain a passport...would you care to tell Princess (as one example) that they're wrong
[size=large]NOTICES
Passports are required for international travel and for all air departures to or from the United States. Princess continues to strongly urge passengers to obtain a passport.[/size] Princess Travel Care or Princess Vacation Protection becomes effective upon payment of premium. For departures on or after December 17, 2008, Princess Cruises reserves the right to re-instate the fuel supplement for all guests at up to $9 per person per day if the NYMEX oil price exceeds $70 per barrel. All air prices are subject to change and are not guaranteed until full payment is received by Princess. Baggage fees and other charges may be directly assessed by airlines or airports. Once you are notified of your flight details, contact the airline as needed. Be sure to review the final payment notice for any adjustments prior to making final payment. Refer to the brochure for other terms and conditions and cancellation policy.
This is copied directly from a Princess confirmation this week for a Caribbean cruise round-trip Fort Lauderdale.