Congress has no authority to investigate or prosecute crimes; these responsibilities belong to the executive branch. It has no power to conduct fishing expeditions, and its investigatory authority is supposed to be in the service of legislation. As the Supreme Court warned in Watkins v. U.S. (1954), investigations unrelated to legislative business are an abuse of power that “can lead to ruthless exposure of private lives.” When congressional investigations seek ruthless exposure of a sitting president’s private life, the harm is not only to persons but to institutions.

Nor is investigating Mr. Trump’s prepresidential activities a legitimate exercise of the House’s impeachment power. The Framers viewed impeachment as a remedy for serious violations of public trust committed while in office. As Gouverneur Morris told the constitutional convention, impeachment would punish the president “not as a man, but as an officer, and punished only by degradation from his office.” Alexander Hamilton likewise observed in Federalist No. 65 that impeachment involves “those offenses which proceed from the misconduct of public men, or, in other words, from the abuse or violation of some public trust.”

The House Judiciary Committee has embraced this interpretation several times.