Congress can enforce its own orders against recalcitrant witnesses without involving the executive branch and without leaving open the possibility of presidential pardon. And a Supreme Court majority would find it hard to object in the face of two entrenched legal principles. First is the inherent power of Congress to require testimony on matters within its legislative oversight jurisdiction. So long as Congress is investigating issues over which it has the power to legislate, it can compel witnesses to appear and respond to questions. That power has been affirmed over and over in prosecutions for contempt.In modern times, this congressional...