From U.S. Customs and Border Protection webpage https://help.cbp.gov/app/answers/det....-territories:

"U.S. Citizens and Lawful Permanent Residents...who travel directly between parts of the United States, which includes Guam, Puerto Rico, U.S. Virgin Islands, American Samoa, Swains Island and the Commonwealth of the Northern Mariana Islands without touching at a foreign port or place, are not required to present a valid U.S. Passport..."