We haven't invested much energy recently in creating institutions that have adequate defenses against this kind of threat model. Our assumption has been that the socialization structure either produces people who are pathologically criminal or are socially responsible. The emergence of a class of social behavior which is "respectable" and despicable at the same time is a threat we need to deal with.
Except you can't - because he didn't violate international nor domestic law. He never waterboarded anyone, nor did he order the waterboarding of anyone.
He worked on legal justifications for the use of torture, which is not an area of international law that's well defined. He didn't make policy nor law, he spun law so that it fit existing policy.
I won't disagree that what he has done is despicable, but what exactly would you charge him with that would actually stick?
Tossing one tenured professor out is a simple thing. After all like you said, it's not written down in the constitution.
The problem with removing tenure is that it destroys trust in the tenure system. If one professor is stripped of tenure for being controversial, then no one is safe. For this reason the only way to lose tenure is to do something illegal, since that's really the only line you can draw that doesn't move very much.
Tenure is an all or nothing deal. The entire effect of protecting your faculty is completely nullified as soon as you violate your principle for one guy. The floodgates open and suddenly every prof that's doing something controversial becomes a target.