My fellow constitutional law scholars have offered a wide variety of comments about the impeachment of President Donald J. Trump, but none have asked or attempted to answer the following fundamental question: what level of proof must the managers of the House of Representative meet during Trump’s trial in the Senate? In brief, a simple majority of the U.S. House of Representatives has charged President Donald J. Trump with two high political crimes: abuse of power and obstruction of Congress. Let’s assume for the sake of argument that these forms of political misconduct are impeachable offenses. (Are they?) If so, what burden of proof must the House managers meet during the Senate show trial in order to prove that President Trump committed either of these political crimes? Should it be “proof beyond a reasonable doubt” (i.e. the highest burden of proof in our common law system of justice), or should it be “preponderance of the evidence” (or “more likely than not,” a much less demanding evidentiary standard), or should it be an intermediate standard like “clear and convincing evidence”? Also, who decides what the burden of proof for impeachment trials should be? The Senate or the Chief Justice of the Supreme Court?