We know he's a strategic, goal-oriented guy so one has to wonder what his objective is with this tweet.
He has plenty of channels to get a message to Sessions without putting it in the public eye, so it appears the goal here is to influence public opinion in some way.
I wouldn't be surprised if the goal weren't psyops.
Just saying, the psyops can play on several levels, and it is entirely possible that Sessions is a sacrificial pawn (although I doubt that is the case).
If nothing else, the recent tweet goes toward making "investigation into FISA abuse" a foregone conclusion. The DEM narrative has been that there is nothing to investigate.
Trump is pissed at all the covert spying on him and his team that has gone on and would like to see someone prosecuted for it.
He is particularly frustrated by his AG, Sessions, who set the wolves upon him by creating a situation that culminated with the appointment of Mueller, appears unwilling to set a similar pack of wolves upon Team Hillary/Obama.
He's so pissed about this, when he things about it, it makes him furious. Eventually lashes out on Twitter to express his *utter frustration*.
Non-Obvious Answer
All Trump's twitter posting is all fake. He's secretly working with Sessoins, and we need to Trust Sessions as we've been told by Q. And we need to trust that the poeple interpreting his cryptic messages are right and that a giant swamp draining operation is secretly underway
Trump, under this non-obvious interpretation is taking time off from arresting his enemies to tweet pretend anger at Sessions to keep his real enemies off balance.
Come on, really?
#DrainTheSwamp, #FollowTheRabbit, #TheComingStorm ... never comes.
Maybe he knows that the report that Obama’s guy is going to come out will be in his favor, and he is trying to drive home the fact already that this guy is indeed Obama’s guy.