Cboldt brought up Vacancies Act last night.
Murky if AG fired
Process is convoluted
But possible avenue
If Pres Trump fires Sessions (as opposed to Sessions resigning), the Vacancies Act does not appear to apply so the statutory succession for DOJ would kick and make Rosenstein Acting AG. That would make bad things worse so Pres Trump would then have to fire Rosenstein also (and Rachel Brand would become Acting AG). This would drive the Congressional bed-wetters and never-Trumpers over the edge and possibly lead to a Watergate-style select committee and a new independent counsel law. So I suspect that the WH is thinking that getting Sessions to resign would be much better (as then the Vacancies Act would apply and Pres Trump would have more options for Acting AG and would not need to fire Rosenstein). Either way, he can get an Acting AG in there and not worry about confirmation of a permanent replacement for a long time.