It's unclear from Trump's tweet which of his proposals would have kept the Somali student, a refugee with permanent status, out of the country. In fall 2015, Trump pledged to kick all Syrian refugees out of the country and to bar others from entering. Days before the election, Trump said that he would not push out refugees without the consent of the community where they would be resettled.

In December 2015, he called for a ban on allowing most foreign Muslims into the country. His running mate and top aides now say that he has abandoned that proposal, even though it is still posted on his campaign website.

This spring, Trump shifted his rhetoric toward targeting countries instead of religion, saying that he would temporarily suspend “immigration from some of the most dangerous and volatile regions of the world that have a history of exporting terrorism.” In August, he called for “extreme, extreme vetting” of all immigrants that would include a Cold War-style ideological test to ensure that an immigrant's views and values align with American ones.

Authorities have not established a motive in the attack at Ohio State. But the law enforcement investigation increasingly is focusing on the possibility that Artan was motivated by radical or terrorist influences, though he had no known contacts with the Islamic State or other overseas terror groups, a U.S. official said.