This is what CBP says:
Land or Sea Travel: U.S. citizens entering the United States by land or sea are required to present a valid WHTI-compliant document, which include:
- U.S. Passports
- U.S. Passport Cards
- Enhanced Driver's Licenses
- Enhanced Tribal Card (ETC)
- Trusted Traveler Cards (Global Entry*, NEXUS, SENTRI, or FAST
- Military Identification Cards (for members of the U.S. armed official maritime business)
With all of that said, I’ve had family members cross with a regular DL and birth certificate recently. I guess it depends on the agent you get at the border.