It’s not that difficult for Trump to point out the Judge’s connection to La Raza and an example or two of actions by the court that are biased. Also, in agreement with Newt, I would parade a half dozen Trump University grads that endorse the courses and have been successful.
He did give examples of rulings that he found objectionable. Like the plaintiff drops the case, but the judge allows a substitute plaintiff to pick it up. He also pointed out that the NY AG was "shopped" and "bought." AG's in Texas, Florida and elsewhere rejected the case; and the outfit that got the NY AG to pick it up, donated to the NY AG's election fund. Tapper claimed to be ignorant of that fact.
Trump could do a better job of rebutting the contention that his objection the judge is based on any racial bias on Trump's part. The objection is favoritism toward Mexicans on the judge's part; and the judge's potential to biased against Trump based on the judge's perception of or objection to Trump's immigration and border policies.
I don't think it matters - the subject is going to be lost in the weeds long before it could affect an election contest.