It’s hard to think of a violation of separated powers as naked as that being attempted by the Senate Democrats against Justice Clarence Thomas over his friendship with the billionaire Harlan Crow. Or to think of an answer as trenchant as that with which Mr. Crow’s lawyer has responded to the chairman of the Judiciary Committee, Senator Durbin. It opens what could be one of the great constitutional battles in the history of our Republic.

That tussle turns on whether Congress can bring the Supreme Court to heel. Mr. Crow’s attorney, Michael Bopp, argues that “Congress does not have the constitutional power to impose ethics rules and standards on the Supreme Court.” It is true that Congress has the power to impeach justices and to carve out their jurisdiction and even set their number. The separation of powers would be offended, though, by binding them to a code of conduct.

Mr. Bopp also warns that Congress’s fingerprints on the high court could  “risk inserting political influences into the Court’s affairs and interfere with the Court’s decisional independence.” We have no doubt that Senators Durbin and Whitehouse, who are leading this charge, would enjoy a greater say in the business of this conservative leaning court. The Framers sought to insulate the Supreme Court from the political, not infect it with politics. 

As Mr. Bopp notes, the Supreme Court is distinct from all other federal tribunals because it is a creature of the Constitution, not Congress. Democratic lawmakers are making much of the fact that lower court judges are bound by a code of conduct that does not touch the justices, but that distinction is not one drawn by Chief Justice Roberts or Justice Thomas. It was the brainchild of Hamilton and Madison. 

“Like the President,” Mr. Bopp  explains, the “Court is the head of a co-equal branch, and derives its powers directly from the Constitution, not from an act of Congress. That means that Congress cannot insert itself into how the Court executes its duties.” These are the “foundational principles of separation of powers.” Just as Congress can impeach the president but not tell him how to work, it can remove justices but not remonstrate them. 

If, then, as “there is no enumerated power that endows Congress with the authority to regulate the Supreme Court’s internal affairs,” Messrs. Durbin and Whitehouse are mounting a campaign that is crosswise with the Constitution and an intrusion —  as of yet, merely preliminary — on a coequal branch of government. We  noted the “invitation to a hanging” Senator Durbin issued to the Chief Justice. That danger was averted. The senator is undeterred.  

Mr. Crow could have stayed silent or mounted a merely personal defense of his friend. Rather, he chooses to join a fight where his only personal stake — one of principle —  is the same as every other American. What he labels a “larger campaign to target and intimidate Justice Thomas” is not only that, but also an effort to “frustrate the independent exercise of the Court’s authority.” In Mr. Crow, the court appears to have found a worthy champion.