No, they're not going to do that because they WANT ISIS to attack us more.I've mentioned this before, but I'll mention it again.
I have a strong feeling that these folks were on the watch list already, problem is until they do something traceably illegal there isn't a hell of a lot the gov can do to protect us without trampling on American's rights. This is why a number of folks want to shut down immigration and refugee influx (at least until we sort out the vetting system) because once they are legally here, there is pretty much nothing the gov can do until it's too late.
I believe they can detain someone for "suspicion of terrorism" but they can't legally arrest them nor keep them off the streets for it, and of course, the current admin isn't even going to do that because they believe that such things cause ISIS to attack us more, (though I personally disagree with that particular premise.)