The highest duty of an American diplomatic or consular officer is to protect citizens of the United States in lawful pursuit of their affairs in foreign countries. The document issued in authentication of the right to such protection is the passport.
Broadly speaking, the Department issues two kinds of passports — those for citizens and those for persons who are not citizens. Citizens’ passports are ordinary and special; aliens’ passports are for travel in the United States and for qualified protection abroad of those who have taken the first steps to become American citizens.
The citizen’s passport is the only document issued by the Department of State to authenticate the citizenship of an American going abroad. The Act of August 18, 1856, makes the issuance to one who is not a citizen a penal offense if it is committed by a consular officer. Before this law was passed the Department did not issue the document to aliens; but it was permitted to this government’s agents abroad sometimes to issue it to others than American citizens. The Personal Instructions to the Diplomatic Agents of the United States of 1853 said:
They sometimes receive applications for such passports from citizens of other countries; but these are not regularly valid, and should be granted only under special circumstances, as may sometimes occur in the case of foreigners coming to the United States.