There should be no path to the White House that includes destroying the nation’s confidence in the rule of law.

Unfortunately, Donald Trump, the presumptive nominee of the Republican Party, is doubling down on his wrongheaded attempt to trash a federal judge in San Diego presiding over two class-action lawsuits against Trump University by former students who claim they were defrauded.

U.S. District Court Judge Gonzalo P. Curiel was born in Indiana to parents who immigrated from Mexico. Early in his career as a federal prosecutor, Curiel had to spend almost a year in hiding on a naval base, protected by U.S. marshals, because he was targeted by the Mexican drug cartel he was trying to take down.

Trump says Curiel cannot be impartial in the Trump University cases. The candidate claims the judge’s Mexican ancestry would make him biased against Trump, who wants to build a wall on the Southern border.

On “Face the Nation” Sunday, host John Dickerson asked Trump whether the same reasoning would make a Muslim judge similarly biased because of Trump’s proposed ban on Muslim immigration. “It’s possible, yes,” Trump said. “Yeah. That would be possible, absolutely.”

At some point, Trump must say how he will keep his considerable business interests separate from his presidential aspirations. But right now, he must reassure the nation that as president, he would respect the independence of the judiciary, a cornerstone of our constitutional system.

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It’s perfectly fine to criticize judges for unpopular rulings or just dumb ones. It’s a national tradition. And if a case is mishandled, there are ways for both sides to get their claims reviewed. But Trump didn’t say that the judge overseeing the Trump University case misread a statute, erroneously disregarded precedent or blindly followed a mistaken legal theory. He attacked the very integrity of Curiel — and by extension, all judges — with his insinuation that impartiality is abandoned if the judge is offended by the litigant’s political views.

Judges are representative of our democracy; it’s important to have racial, ethnic, gender and religious diversity on the bench. For a presidential candidate to try to delegitimize a jurist based on his or her background is contemptible. — The editorial board