By firing him now perhaps all this Clinton corruption that is oozing out finally can be stopped and covered back up. Trump has kept Mueller on because Mueller is useful, unwillingly useful to be sure, but useful. If all this exonerating stuff and the Clinton stuff comes through his office as a result of his investigating Trump, it is hard for MSM to discount it. MSM can only ignore it for so long and the ignoring makes it easier to bring this stuff to some sort of Justice. Then, when some of the left’s heroes are defendants, they can scream and beat their heads on the wall and it will be too late. No one at all will believe the MSM. The Left will still support it and cry Unfair! but everyone will know.
Apparently the possibility that some intriguing things might be going on behind the scenes doesn't even cross the minds of a lot of people here.