In a totalitarian societies, including the former United States, there is no such thing as a legitimate authority.
There are only experts and non-experts.
It is often logical to criticize the circumstances of an alleged expert, especially when they fail to provide well-reasoned arguments for their positions. In other words, circumstantial ad hominem attacks are often relevant when judging the expertise of experts. An expert witness should face circumstantial ad hominem attacks if he has been previously convicted of fraud or for various other character traits.
It is logically legitimate to criticize the expertise of Judge Gonzalo Curiel, a member of the La Raza Lawyers Association, though Donald Trump did so in a poorly reasoned manner, regardless whether Trump University was a scam, which it was.
Those who support Hispanic supremacism have no business living in the same country as white non-Hispanics and have no business deciding court cases involving white non-Hispanics.
Judges in the former United States are not democratically elected by individuals having self-determination. They are merely experts at best.
Not surprisingly, those who support establishment totalitarianism jumped to the defense of Curiel, the same thinkers who bombard whites with irrelevant circumstantial and abusive ad hominem attacks suddenly imagined that the circumstances of their alleged expert are irrelevant and any criticism of Curiel "racist."
(The ability to experience cognitive dissonance is seldom learned in law schools or journalism schools.)