It’s an argument about legal technicalities. I don’t know why he’s getting involved, but it’s possible to disagree with the probe without finding it violates the Constitution.
Agreed,
It's not that a probe by a Special Prosecutor or Special Counsel is in and of itself a violation of the Constitution.
The problem is that this particular probe is being conducted in pursuit of a political agenda instead of justice.
It has been weaponized by a Special Counsel running amok in an attempt to unfairly damage or destroy a presidency.