[dragonwriter]

Suggesting that he is biased based on nothing other than his race is racist. Presenting actual evidence of bias and identity-based motivation might not be racist, even though it might attribute bias to race, but that is a different story.

Trump has directly said that the judge must be biased, because of his ethnic heritage and the supposed "fact" (which isn't actually a fact, but anyway) that Trump is "building a wall" -- that is, the claim actually being made by Trump is that it is impossible for any person of Mexican heritage to not be biased against Trump because of Trump's specific policy stances.