Three people vs the 3,066 Americans killed by direct Islamist terror attacks on US soil, mainly by foreign born Islamist Muslim terrorists. 

Doesn't pencil out. 

As for Mother Nature, we can't ban her U.S. entry. 

But oh yes indeed, we can ban travel of foreign people. Trump is right. 

Next?

http://www.start.umd.edu/pubs/START_AmericanTerrorismDeaths_FactSheet_Oct2015.pdf