The President has the authority to stop immigration and has done so before. Title 8, Chapter 12, U.S. Code 1182 clearly states "The President – may suspend the entry of all aliens, or any class of aliens as immigrants or non-immigrants, or impose any restrictions." Even President Obama stopped Iraqis from entering the U.S. for a time. In November 1979, during the Islamic takeover of our embassy in Terran, the Democratic President, Jimmy Carter, invoked the Immigration and Nationality Act of 1952 and signed Executive Order 12172 that banned all Iranians from entering the country, expelled Iranians already in the country and added extra border screening. President Carter also canceled visas issued to Iranians and made 50,000 Iranian students register at the immigration office. None of that was unconstitutional.