I think you're right. Trump is hinting the "list" idea.
What I don't understand is...
FBI has Achmad Saleem whatshisface on a watch list or even Bubba Rebel whatshisface. Then they try to buy a "Powerful Rifle". Why not let them buy the rifle and then watch the crap out of them even more to catch him in the act?
An indefinite watch list or no fly list with no real crime is just the slippery slope towards Orwellian Totalitarianism.
I agree, we have seen what fearless leader did with the IRS, I can see anyone who opposes the government is marked as a terrorist and thereby lose a constitutional right without any due process.