As the Select Committee to Investigate the January 6 Attack prepares to stage a show trial of Donald Trump on Capitol Hill this week, I have filed a lawsuit challenging the Select Committee’s gross violations of the Constitution’s separation of powers. Yes, congressional committees do have the power to investigate. Yet, they can only do so in pursuit of a “legislative function,” e.g., to enact new rules, regulations, or policies. What settled law explicitly rules out is the pursuit of a “judicial function” in which a congressional committee seeks to act as judge, jury, and executioner. That clearly violates the...