Here is a more detailed explanation of the law…

Under U.S. law (8 U.S.C. § 1185(b)), all U.S. citizens—regardless of whether they hold multiple nationalities—are required to use their U.S. passport when entering and leaving the United States.

Key Legal Points:
1. *The Passport Requirement*: The U.S. government mandates that American citizens use their U.S. passport for travel in and out of the country. This is to establish the traveler’s legal status as a U.S. citizen and avoid potential complications with immigration.
2. *Dual Citizenship Considerations*: A U.S. citizen who holds another nationality may use their foreign passport when entering or exiting the other country of their nationality, but they must always present their U.S. passport at U.S. ports of entry and departure.
3. *Customs and Border Protection (CBP) Enforcement*: U.S. Customs and Border Protection (CBP) officers routinely check for compliance with this rule. Attempting to enter the U.S. with a foreign passport can lead to delays, additional scrutiny, and in some cases, denial of entry until the U.S. passport is presented.
4. *Legal Consequences*: Failure to comply may result in fines or administrative action, though most enforcement involves requiring the traveler to prove their U.S. citizenship before being allowed entry.

*Common Misconceptions*:
• “I can enter with my foreign passport because it has a U.S. visa.” → Incorrect: If you are a U.S. citizen, you are not considered a visa holder, and your U.S. passport is required.
• “*I can leave the U.S. on a foreign passport.” → Incorrect*: Airlines and CBP require U.S. citizens to use their U.S. passport to board international flights departing from the U.S.

*Conclusion*:

If you hold multiple citizenships, you must use your U.S. passport when entering and exiting the United States. However, once outside the U.S., you are free to use your other passport(s)