He claims Judge Gonzalo Curiel's Mexican heritage is a conflict of interest, but his lawyers haven't filed a legal motion about it—for good reason.
Why not? There is a very simple answer. Here is the question and answer reported in the New Republic.
Donald Trump has repeatedly argued that Judge Gonzalo Curiel has been unfair to him in the Trump University lawsuit and should recuse himself from the case. The presumptive Republican presidential nominee claims that Curiel’s Mexican heritage and his membership in the San Diego La Raza Lawyers Association creates an “inherent conflict of interest” because, as Trump put it in an interview with CNN, “I am building a wall.” But even Trump’s own lawyers appear to know better.
Trump has a simple remedy for this alleged conflict of interest, but he has not invoked it. He could direct his attorneys to file a disqualification motion pursuant to the United States Judiciary Code, on the ground that Curiel’s “impartiality might reasonably be questioned.” Given how strongly Trump feels about the situation—he has even called for an investigation of Curiel—why haven’t his lawyers already taken the necessary steps to disqualify the judge?
The Federal Rules of Civil Procedure require lawyers to certify that their motions are “warranted by existing law or by a nonfrivolous argument for extending, modifying, or reversing existing law or for establishing new law.” The “existing law” could not be more clear that a judge’s background provides no legal basis for seeking disqualification. There is a long line of precedents applying this principle to African-American, Jewish, female, Catholic, Mormon, and gay judges. Any lawyer who brought a motion on similarly spurious grounds—or who tried to argue for changing the law to allow ethnicity-based disqualification—would be subject to sanctions including monetary penalties, censure, and even referral to the disciplinary authorities.
And Trump's high-powered lawyers are not about to risk that damage to their own reputations. They know better, and, presumably, they might have said so to Trump. If that is in fact the case, then Trump has only two alternatives: keep the attorneys and continue to blast away with racist rhetoric or fire the attorneys and hire lawyers who care less for their reputations.
Rule of law 1, Trump 0.