My fiance's parents are going on a cruise to the Bahamas.
Now, as I understand it, they could go for the cheaper passport card, but some form of passport would still be required. They think they won't need a passport since they will leave port in South Carolina cruising to the Bahamas and then returning to the same port.
Who is correct? Me or my fiance's parents?
In principle, maybe not. In practice, yes, they need a passport.
For a closed loop cruise (one which leaves and enters through the same port), a US citizen does not need a passport to re-enter the country. They do need you to present some sort of proof of identity and citizenship, such as a birth certificate or government issued ID.
That said however, it is highly likely that the passport will be needed in order to disembark from the ship at a port of call - and furthermore many cruise lines, in order to reduce their administrative load, will simply require all passengers to present a passport before boarding.
Specifically in the case of the Bahamas, a passport, passport card, or WHTI compliant drivers license is required for entry.
In the end, the best and most important thing to do is check with the cruise line, but it's most likely that the answer is going to be yes - especially if they have any intention of, y'know, getting off the boat. Which they should! In that case, they need passports, or, if they are residents of Michigan, New York, Vermont or Washington, they could get by with an Enhanced Driver's License.
The best source of this information is to ask the cruise company running the cruise.
Some cruises that start from and end in the US do NOT require a passport, whilst others do. Even if a passport is not required, additional documentation may be required when returning to the US, such as proof of citizenship (birth certificate, driver's license for proof of ID, etc).
The cruise company will know the details of what is requires for the specific cruise that they are on.
