M is looking for an exit strategy after finding absolutely nothing, the one scenario they did not consider.
I think M is looking to get fired and then claim the final "evidence" was removed from his offices by PDJT operatives after he was removed, which will "prove" that President Trump is guilty of "something" but nobody will ever know what that something was.
M will not be able to say what "it" was because he was fired before he could connect all the dots and his "integrity" will not allow him to speculate.
They will be able to beat that drum forever.
His exit strategy should be to do a thorough investigation and then announce that despite the thorough investigation he’s found nothing that a reasonable prosecutor would prosecute. I have a fantasy that that’s exactly what he’s doing. In order to retain credibility with the Dems he’s got to do a thorough job. But if he can’t find anything then that’s just the way it is.