Troops in the US and other NATO countries could stop the influx of people who will bring with them disease and radical jihad.
Right now NATO has to face Russia which is currently invading another country, and doing what they are supposed to do.
As far as terrorists, each nation’s individual police and military forces deal with them when they are discovered operating inside their borders, and of course the military doesn’t need to be screening me for infectious diseases, we have people that handle that kind of thing.