Don’t blame Brett Kavanaugh when he demurs at his confirmation hearing from answering questions on legal issues that might come before the Supreme Court. It’s the senators who will be in the wrong, for demanding commitments that no judicious nominee could provide. To answer “direct questions on stare decisis on many other matters, including Roe and health care”—as Minority Leader Chuck Schumer has called for—would itself be disqualifying.

That principle has come to be called the Ginsburg Standard, after Justice Ruth Bader...