. . . and finding out about huge tax evasion, and unregistered representation of at least one foreign government (a moderately hostile one at that). . . 

So, assuming the charges can be prosecuted with success, what's your objection to him catching such a criminal????

Isn't it good and important that Manafort and his minion were caught?  Would you rather they get away with doing those things scott free?  Should they walk?  Is that what you're saying?

One good thing is that maybe Mueller is paying for his investigation by getting Manafort first.  The seizures and tax penalties and interest should fund the Special Counsel's office for awhile.