Citizens

Everyone within the jurisdiction of the United States is protected by most of the guarantees and safeguards of the Constitution. A U.S. citizen traveling abroad retains the protection of the United States. If property of an individual is stolen while he or she is in a foreign country, the United States consul can lend him or her money to return to the United States. U.S. citizens, of course, must observe and obey the laws of other countries while they are visiting, but if a U.S. citizen is arrested, a representative from the U.S. ambassador's office can visit him or her and inform the foreign government that the treatment of the U.S. citizen will be scrutinized.

Unlike citizens of other countries, U.S. citizens are entitled to enter into, and to depart from, the United States, and to obtain a passport from the government. The passport certifies to foreign nations that its holder is entitled to all of the protection afforded by the U.S. government. The right to enter and leave the United States is so fundamental, however, that a citizen cannot be prevented from coming into the United States merely because he or she has no passport. Even if someone departs from the country without obtaining a passport, knowing that he or she should have done so, he or she must be permitted to enter upon returning if a birth certificate or expired passport is presented, or if the person takes an oath as to his or her citizenship.

However, the U.S. government can prohibit its citizens from traveling in designated countries

Immigrants take an oath of citizenship in a 1990 ceremony held on Ellis Island in New York City. Naturalized citizens have all the rights of a native-born U.S. citizen with one exception: they cannot serve as president of the United States.
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that are hostile to the U.S. and perilous to U.S. citizens. The passport of a person who ignores these restrictions can be revoked, and such a traveler can be denied protection by the government.

A naturalized citizen has all of the rights of a native-born U.S. citizen but one: He or she can never be president of the United States. Article II of the Constitution provides: "No person except a natural-born Citizen, or a Citizen of the United States, at the time of Adoption of this Constitution, shall be eligible to the Office of President."