“Obama and crew have already done it”
That is true (along with previous presidents) but that is de facto. Sessions is talking about de jure — Obama codifying it with law; his personal decree. If it stands, our Republic is over, much like when Caesar crossed the Rubicon.
So what is the feckless bunch in congress going to do about it? Nothing probably. These unrepresentative gelding need to grow a pair. They won’t.