IMHO, he's lying. He is, after all, a longtime Democrat, who has admitted "we'll let in the good ones," as if such a filtering process could be done in less than many years. We're set amid that awful choice in which we choose to institute dictatorial and potentially unjust (deporting legal immigrants and their citizen children (however illegally conferred; it's not the kids' fault), confiscating property, etc.) emergency powers to survive (street battles to gather them). Were we to commit to this as a nation as a matter of war powers subsequent to invasion, I'd rather have a real Sulla, calm, quiet, proven, and determined, as opposed to this dishonest huckster.
He hasn't leveled with anybody as to what he would really do and how; he just promises to get it done.
Trump can very possibly force Congress to join him just by the power of public opinion. Reagan did, often and had less of a celebrity presence than Trump did. So, no nothing is "underhanded." It's all above board and that's what bothers so many of the opponents.
How does this make him different from any of the other pasty faced limp-wristed politicians?