... and what I can't wrap my head around is why? If Session's was a soldier of the Deep State Establishment, GOPe, or whatever...Why did he endorse Trump instead of one of the other more conventional and likely GOP winners so early???
Nobody except @DCPatriot thought he could win the nomination at that point
...Was it just to sabotage Trump after he won the Presidency? Who thinks like that? Who structures their future on the destruction of their party? It makes no sense to me.
I personally have no opinion on whether or not Sessions has "nefarious intentions" towards Trump.
But to answer the specific question you just asked, I suppose one possible answer is that Sessions may have simply changed his mind on Trump. Perhaps he really liked Trump early on, but became disenchanted with him over time to the point where he now dislikes him intensely, and regrets his early support.
I'm not claiming that is actually the case. I'm simply pointing out that Sessions being an early supporter of Trump does not preclude the possibility that he opposes Trump now, and is now an ally of convenience for the GOPe/deep state.