Soon after issuance of Trump's January 27, 2016 Executive Order 13769, titled “Protecting the Nation from Terrorist Entry into the United States by Foreign Nationals,” which (among many things) blocks visa approval, U.S. admission, and other "immigration benefits" to people from a list of countries considered to support terrorism, namely Iraq, Iran, Libya, Somalia, Sudan, Syria and Yemen, plus others to be potentially added later, an important question was raised: What about people with dual citizenship? If, for example, someone holds a passport from both Iran (which is on the barred list) and Germany, could the person use the German passport for U.S. entry?
The Department of State (DOS) initially said no. CNN quoted a State Department official who said, "Travelers who have nationality or dual nationality of one of these countries will not be permitted for 90 days to enter the United States or be issued an immigrant or nonimmigrant visa."
In fact, the U.K. Telegraph reported that former Iraqi ambassador to the U.S. Lukman Faily was planning to travel to Washington for a conference on fighting the Islamic State, but was told by the U.S. embassy in Baghdad that he was included in the ban, despite also holding a British passport.
However, by February 2, 2017, the DOS had partially reversed its position. It issued an Emergency Alert stating that the executive order does NOT restrict the travel of dual nationals from an unrestricted country who have a valid U.S. visa in their passport from that country. In addition, the DOS alert states that U.S. embassies and consulates around the world will continue to accept and make decisions on visa applications from otherwise eligible applicants who apply using a passport from an unrestricted country, even if they hold dual nationality from one of the countries on the restricted list.
Also according to CNN, the U.S. government has informed airlines that dual nationals holding a passport from an approved country would be allowed to travel to the United States.