We should heed closely what Donald Trump has been saying about U.S. District Judge Gonzalo Curiel of San Diego—perhaps more so than anything else he has said or done to date. The prospect that a President Trump might defy the judiciary and the rule of law, together with his vows to violate international treaties and his disrespect for domestic laws, may make him the most dangerous candidate in American history.

There are so many things to deplore about Trump’s recent attacks on Curiel it is difficult to know where to begin. Trump has asserted that Curiel is unfit to hear two lawsuits against the now-defunct Trump University because “he’s a Mexican” (false—Curiel was born in Indiana)—and thus probably biased against Trump’s plan to “build a wall” on the Mexican border. Trump has also suggested that any judge of Mexican, or of Muslim, heritage would be biased against him. He has declared that he’s “getting railroaded” by a “rigged” legal system and suggested he “will come back in November” to change things.

This is racism and ethnic and religious bias. It is a deplorable elevation of Trump’s raw financial and political self-interest above the law and the national interest. But mostly what we should deplore—and fear—is this: Such a brazen presidential attack on the rule of law, by a man of such a belligerent temperament and crude sensibility, could portend defiance of court orders by a President Trump.