While a lot of people think what Trump said is extremely out of what United State legislators stand for, current Senate and President passed and signed HR-158[1] which bans European citizens that visited Iran, Syria and Iraq in past 5 years from getting into United States without a visa. This is going to apply to pretty much any dual citizen of Europe that visit their families back home in every couple of years.

Obviously asking for someone's religion is the most stupid way of filtering terrorist, when governments decide to do something like that they discriminate based on place of origin.

[1] https://www.congress.gov/bill/114th-congress/house-bill/158