“If he fires him they will not confirm another which essentially leaves Rosenstein as AG.”
Not necessarily. Trump can appoint an interim AG and they can start the job immediately, as long as the nominee has already been confirmed by the Senate for some other Executive branch position. This is the loophole Trump needs to use to pull the rug out from under the Senate’s threats.
No, Trump can not appoint an interim AG. Mitch never declares the Senate out of session. There is always at least one Senator at the Senate. Mitch will not allow Trump to make an interim appointment.