"Mueller’s pursuit of the money trail is likely what Trump fears the most in the Russia probe, not collusion."

Exactly.  Finances are Trump's Achilles heel.  He has done everything in his power to hide his finances, but Muller hopefully will put an end to that crap.  It may very well turn out his finances are squeaky clean, but I think just about everyone (even his supporters) knows that will not be the case.

There is a stinking skeleton or twenty hiding in that closet . . . and Muller will certainly go there.