Donald Trump’s claim that he couldn’t get fair treatment from Judge Gonzalo P. Curiel because the judge’s Mexican heritage is in conflict with Trump’s comments on the campaign trail is absurd on its face.

Trump originally claimed of the judge that "he’s a Mexican," which is false. Then he backpedaled, as he often does, and amended his statement to say that because Curiel is "of Mexican heritage," the judge has a "conflict of interest" in presiding over a lawsuit filed against Trump University.

"I’m building a wall. It’s an inherent conflict of interest," Trump said, referring to his campaign promise to construct a wall along the U.S.-Mexican border to keep out illegal immigrants.

"Claiming a person can’t do their job because of their race is sort of like the textbook definition of a racist comment," said U.S. House Speaker Paul Ryan.

The speaker is right.

If Trump wanted to credibly claim bias, he should have limited his criticism to the fact that Curiel was appointed by a Democratic president, Barack Obama. But "limit" does not seem to be in the Trump vocabulary. Or, if it is, it’s not one of the things he does very well – at least when it comes to himself.

Had Trump restricted his remarks to the fact that Curiel is a Democratic appointee, his claim would at least have a modicum of credibility.

The fact is, our society assumes that bias is part of the package judges take to work with them each day, which is one reason there is such a hue and cry over the Senate’s refusal to hold a hearing on President Obama’s nomination of Judge Merrick Garland to the U.S. Supreme Court. We take it for granted that a judge appointed by a Democratic president or governor will have one set of values, while a judge appointed by a Republican will be predisposed to a different set. That’s a reasonable assumption, too, given that judges don’t cease to be human once they put on the robe.

But nobody makes the argument that a judge can’t hear an antitrust or workplace discrimination case because he or she was appointed by a president or governor from a certain political party. We also assume that whatever biases jurists take to work with them is balanced out by a judge’s demonstrated ability to do their duty and uphold the law. They are elevated to the bench for a reason.

Of course, Trump may have given rise to a new twist on an old legal saw about how to argue a case. "When the facts are against you, argue the law," goes the first part of the adage. "When the law is against you, argue the facts. And when the facts and the law are against you, just argue."

The Trump variation on that might well be amended to: "When the facts and the law are against you, argue the judge."