What does a US citizen need to reenter the US?
What does a US citizen need to reenter the US? All U.S. citizens need U.S. passport books if re-entering by air. Land and sea border crossings accept additional travel documents, such as U.S. Passport cards and Trusted Traveler cards. Child travelers have additional options - see the Traveling with Children section.
How long can a US citizen stay out of the US?
You can travel abroad for as long as you'd like without any risk of losing your U.S. citizenship. And if you plan to stay outside of the United States for longer than a year, you won't need a re-entry permit in order to return, as is the case for green card holders (permanent residents).
Can I enter a country with one passport and exit with another?
U.S. nationals, including U.S. dual nationals, must use a U.S. passport to enter and leave the United States. U.S. dual nationals may also be required by the country of their foreign nationality to use that country's passport to enter and leave that country.
What is the penalty for U.S. citizens entering leaving the US on a foreign passport?
There are no penalties. The customs officials might be furious but the only thing they can do is confirm you're citizen and let you back in. As for leaving the US, the US doesn't have exit checkpoints so you can leave on any passport.