> the executive branch followed certain norms around this, until this administration

Which norms? Which administration didn't act differently than all others? Reagan firing the FAA unionizers was a new one.

Obama said he couldn't “waive away the law Congress put in place.” DHS went and legalized a few million anyway, years later. Sounds very familiar, but somehow different?

I'm not sure what you're talking about, but it sounds awfully revisionist.