Hearings began this week on whether the 14th Amendment disqualifies Donald Trump from running for president in 2024 because of his actions around the Jan. 6 attack on the U.S. Capitol.

On Monday morning in Denver, a historic five-day evidentiary hearing began for a lawsuit filed against Trump by six Republican and unaffiliated Colorado voters represented by the watchdog group Citizens for Responsibility and Ethics in Washington (CREW).

A similar hearing is set for Thursday in Minneapolis.

CREW President Noah Bookbinder has said that his organization brought its suit in Colorado because “it is necessary to defend our republic both today and in the future.” The group’s complaint accuses Trump of inciting and aiding the mob at the Capitol two years ago, which he denies. He was impeached on similar charges but acquitted by Republicans in the Senate.