The acting attorney general of the United States is a crackpot.

Matthew G. Whitaker, installed in the job by President Trump to replace Jeff Sessions, was asked in 2014, during an ill-fated run in the Republican senatorial primary in Iowa, about the worst decisions in the Supreme Court’s history. Whitaker’s answer, to an Iowa blog called Caffeinated Thoughts, was chilling.

“There are so many,” he replied. “I would start with the idea of Marbury v. Madison. That’s probably a good place to start and the way it’s looked at the Supreme Court as the final arbiter of constitutional issues. We’ll move forward from there. All New Deal cases that were expansive of the federal government. Those would be bad. Then all the way up to the Affordable Care Act and the individual mandate.”

Reasonable people can differ over the constitutionality of the Affordable Care Act. Maybe there’s some space to debate the New Deal-era cases that cemented the authority of the regulatory state. But Marbury? This is lunacy. For any lawyer — certainly for one now at the helm of the Justice Department — to disagree with Marburyis like a physicist denouncing the laws of gravity.

Decided in 1803, at the dawn of the new republic, Marbury v. Madisonis the foundational case of American constitutional law. It represents Chief Justice John Marshall’s declaration that the Supreme Court possesses the ultimate power to interpret the Constitution and determine the legitimacy of acts of Congress.

In Marshall’s famous words, “it is emphatically the duty of the judicial department to say what the law is.” The untested new Constitution provided that the Supreme Court possessed the “judicial Power of the United States,” but it did not define what that power entailed. ...