Sessions is in the on-deck circle, his firing will happen when trump needs a bigger-than-usual distraction, say, when stormy comes out with a tape or something. Rexxon got shitcanned on the day when trump is likely to be humiliated by a loss of his candidate in pennsylvania (if he doesn't lose, it will certainly be viewed as a defeat anyway since there is no way the repub candidate is going to win by anywhere near 20% which was the trump margin of support.
Of course, it is a multiple choice thing, as there are so many scandals and controversies and inconsistencies that the whole country needs a mulligan.
He uses people like pawns, which should be obvious to anyone, as he either puts a general in important positions so they follow orders readily, or puts a person in that he can jerk around to feed his ego. I cannot imagine people volunteering for his open jobs unless they have some motivation like wanting in on the corruption.