An Impeachment Trial Without Witnesses Would Be Unconstitutional

White found support for his conclusion in the Framers’ understanding of the impeachment process, particularly the arguments by Alexander Hamilton, the delegate to the Constitutional Constitution who devoted the most attention to the impeachment function of the Senate. Contrary to McConnell’s assertion that impeachment is actually a “political process” and that “there’s not anything judicial about it,” Hamilton described the Senate in “Federalist No. 65” as possessing a “judicial character as a court for the trial of impeachments,” and in “Federalist No. 66,” he repeatedly referred to the Senate as “a court of impeachments.”

There is a widespread assumption among Americans that it is perfectly legitimate for the trial to be conducted as a no-holds-barred partisan battle, with senators voting along party lines, rather than impartially deciding the merits of the case. This is contrary to the Framers’ intent. Hamilton regarded the upper chamber as “the most fit depositary” for the impeachment trial because it provided “the necessary impartiality between an individual accused, and the representatives of the People, his accusers.”

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The choice of the Senate made sense for the Framers, who contemplated a republic without strong parties and a Senate whose members —elected by state legislatures until the Seventeenth Amendment was ratified in 1913—were expected to function in a less partisan, more deliberative, and wiser manner than their popularly elected counterparts in the House. The impeachment oath, which requires senators to “do impartial justice,” is not a quaint ritual to be performed with a wink and a nod, but a procedure required by the Constitution because the Framers intended the impeachment proceeding to be run much like a judicial trial.

Senators are thus constitutionally bound to follow what Justice White described as “a set of minimal procedures.” His opinion does not specify their exact contours, except to say that they must be the kinds of procedures a reasonable judge would regard as necessary components of a court trial. Because no reasonable judge would refuse to allow witnesses with personal knowledge of the facts to testify in an ordinary trial, it is the Constitution itself that establishes the right of House managers to call witnesses such as former National Security Adviser John Bolton and Acting White House Chief of Staff Mick Mulvaney. Both men are thought to have firsthand knowledge of the president’s purpose in holding up congressionally approved military assistance to Ukraine after a phone call in which Trump asked the country’s newly elected president, Volodymyr Zelensky, to investigate Joe Biden and his son Hunter.

At least three moderate Republican senators—Mitt Romney of Utah, Lisa Murkowski of Alaska, and Susan Collins of Maine—have indicated their openness to hearing testimony from Bolton and other key witnesses, which leaves the 47 members of the Democratic caucus one vote short of the majority needed to compel testimony from the four current and former administration officials on their witness list. In addition to Bolton and Mulvaney, House managers want to call Robert Blair, a senior adviser to Mulvaney, and Michael Duffey, a top official in the White House Office of Management and Budget who, at the direction of the president, ordered the hold on the military assistance 90 minutes after the phone call. The nonpartisan U.S. Government Accountability Office has ruled that even if the president withheld the aid for national-policy reasons, rather than for personal political gain, his action violated the Impoundment Control Act because the president cannot substitute his own policy priorities for those of Congress.