If he’s worried that we may not find out about collusion and we may have an illegitimate president, he should have been speaking out for a year. At this point, the “illegitimate president” will serve at least half his term. That’s really bad for the country if true and Mueller is doing a terrible job. Odd that McCabe is only now raising concerns that Mueller may not have enough time to finish and hasn’t been urging speed since day one.
More likely, Mueller’s purpose is not to remove an “illegitimate president”, but to run interference into investigations of illegal activity by the DOJ/FBI. In this case, McCabe would be in no rush to have Mueller “finish” his work and would be very concerned about the “investigation” shutting down while congress still has some interest in oversight of 2016 activity.
Mueller’s job may be to seek out and destroy certain embarrassing evidence going back to say, the founding of the Holy Land Foundation.