Donald Trump’s suggestion this morning on Face the Nation that it is possible he couldn’t get a fair hearing from a judge who is a Muslim is the clearest indication yet of why even those rooting for a Republican victory worry about him. We don’t suggest his latest remarks are the only such indication, just, in our opinion, the clearest. They are even clearer — owing to the constitutional prohibition on religious tests — than Mr. Trump’s libels of Judge Gonzalo Curiel. Those hoping that Mr. Trump will find his way to high ground are sick inside.

There are two classic opinions by judges refusing to recuse themselves in cases where their fitness to hear a case has been challenged because of their backgrounds. One was by Leon Higginbotham, then a United States District Judge. His fitness to serve in a civil rights case was challenged because, among other claims, he was black, believed there has been social injustice against blacks in America, and in an address to black historians had used the first person plural pronoun “we.” Plus he had “emotional commitments to civil rights causes of the black community.”

Another was handed down here at New York by Michael Mukasey, also then a United States District Judge. His recusal had been sought by one of the conspirators in the 1993 bombing of the World Trade Center, Ibrahim El-Gabrowny. The terrorist, now doing 57 years in a super-max prison, objected to, among other things, the fact that Judge Mukasey is an Orthodox Jew and a Zionist. Plus, is married to one. Both judges denied the recusal motions. They did so in opinions that are thorough, eloquent, and — in a deeply satisfying way — American.

Here’s how Judge Mukasey summed up: “The basic fact issue in this case is whether El-Gabrowny and the others named as defendants in this indictment made the agreements and committed the other acts charged with the requisite knowledge and intent. That issue will be decided by members of a jury. Even those jurors, who are the only fact finders in the case, will have no occasion to approve or disapprove the views of Jews or Zionists, or the detractors of either or both. Even they will not be asked to make a judgment approving or disapproving any views or beliefs of these defendants . . .”

Judge Mukasey noted the presiding judge’s rulings would be subject to appeal. He refused even to address questions raised about “connections to Israel between me and my wife and our relatives to the third degree of consanguinity,” saying that “to respond to such inquiries is to concede the relevance of the information.” Judge Mukasey saluted Judge Higginbotham’s opinion for identifying what Judge Mukasey called “the fatal evil” of both motions — that their rationale “would amount to, in practice, a double standard within the federal judiciary.”

Someone should get a copy of these opinions to Mr. Trump. It is a telling fact that, at least insofar as we’re aware, he has not actually sought recusal of Judge Curiel (or ever come before a judge who is Muslim). Were he ever to seek recusal on the grounds about which he has been muttering, it is inconceivable that he would prevail. Justice Scalia, in a case involving his duck-hunting pal, Vice President Cheney, felt that since normal practice did not require his recusal, it therefore did not permit his recusal. One of the things about high office of the kind to which Mr. Trump aspires is that one must not permit oneself to be lightly driven from duties subscribed to by the constitutional oath.