I don't think you can be a fair judge of what is an impropriety.
I think I can, actually. Here's the thing. If Trump's Lawyers went into court and said, "Judge Cuzial is a Mexican and can't give my client a fair shake because he wants to build a wall", they not only would be laughed out of court, but they'd be SANCTIONED for doing it. Which is why they haven't done it.