Opinions from law professors are like opinions from anyone else...
True, but this particular law professor is known to be on the liberal side politically. So nobody can say that he loves Trump or Republicans, as being the basis for his opinion.
Opinions from Dershowitz are unlike opinions from anyone else.
Many judges pray at night that they never have to face Dershowitz in appeals court.
In addition to teaching law, Dershowitz has practiced law as a successful defense attorney. In his heyday, the wealthy and powerful hired him.