Can I travel in the US with my foreign passport?
Can I travel in the US with my foreign passport? Can I fly with a foreign passport or Employment Authorization Document Card? Yes, as noted above, the list of approved identification to fly domestically includes foreign government-issued passports and/or a U.S. Citizenship and Immigration Services Employment Authorization Card (I-766).
Can I travel with my old passport after naturalization?
The United States allows naturalized (and other) citizens to become dual citizens with their home countries (though it's not possible for everyone, depending on the laws within said home countries). And if you're a dual citizen, you may not only keep your old passport, but travel with it, if you wish.
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.