I was actually at the rally when he announced this. Trump wants a freeze on immigration from countries that are actively producing a large number of jihadis which, surprise, happens to be predominantly Muslim countries. The premise being, they need more scrutiny and we need time to implement such. Of course I'm sure this whole time he's just been pulling from George W's playbook, acting like an "every guy" who doesn't use big words and wants to appeal to populism.
This is a mountain out of a mole hill. You'd be better off eating less junk food and paying more attention while driving rather than concern yourself with these edge cases.
The problem is that terrorism leads to sectarianism, and sectarianism leads to civil war. Northern Ireland is an excellent example of this paradigm and it has been replicated in Syria.
Many people believe the same threat exists in Europe esp. France.
"...that might arise"? What have we been seeing the last year, when the winning presidential candidate proposed banning Muslims from entry to the US, and as recently as a few weeks ago (and well after the election) said with respect to a Muslim registry that "he would implement that [a registry], absolutely" [1].
Meanwhile, various of his surrogates have in recent days (all after the election) floated the idea that the Japanese internment supreme court decision (never struck down!) could be used to justify this registry.
And go check out his core followers at any of the usual hangouts, like Reddit and Breibart, and you'll hear much, much more extreme views on this issue.
1. http://www.nytimes.com/politics/first-draft/2015/11/20/donal...