He would not rule it out.
Nor should he have. The job of POTUS is to protect and defend this nation against ALL enemies, FOREIGN or DEOMESTIC. If that requires registration, tracking, or internment, so be it.
Right. The Constitution is not a suicide pact. It's fashionable now to carry on about oh-how-awful Japanese internment in WWII was ----- but those Japanese mainly lived right by the shipyards where the Yorktown and other ships were being repaired and refitted and sent right back to sea. Japanese spies could have lost us Midway. I think the internment was entirely appropriate: we knew how to WIN wars in those days, and we've lost that. Now we can't go to war because the whole nation knows we can't ever win. Trump could change that. He reminds me a lot of Teddy Roosevelt --- except of course for the "speak softly" part.