Federal judges have repeatedly and emphatically refused to recuse themselves from cases because of their race or ethnicity. These rulings were driven by two realizations: Ethnically based challenges would reduce every judge to a racial category, which would be racist in itself. And such challenges would make judges vulnerable to recusal motions — for reasons of race, ethnicity, gender or religion — in every case that came before them.

In other words, once these challenges were allowed, there would be no end to them.

The gravity of this matter has clearly eluded Donald Trump, who has cast aside the Constitution and decades of jurisprudence by suggesting both ethnic and religious litmus tests for federal judges. These pronouncements illustrate that Mr. Trump holds the rule of law in contempt.