ALL US citizens will need a passport or a passport card to travel anywhere and by any means outside the United States.Currently, US citizens need a passport if they travel by air regardless of their destination. The new rule now applies to LAND and SEA travel as well.
In the past US citizens have been able to reenter the country from Canada, Mexico and the Caribbean with just a photo ID and a birth certificate or other form of citizenship. The US State Department has been gradually phasing in tighter restrictions and the JUNE 1 rules will bring all travel in line, regardless of destination.
The only exception is children under the age of 16. For travel from Canada, Mexico or the Caribbean they will continue to be allowed reentry with a birth certificate or naturalization paper. Of course children traveling outside North America will still need passports as they always have.