Who are the witnesses?
Republicans have called three witnesses -- one constitutional law scholar and two financial experts.
They are Bruce Dubinsky, a forensic accountant; Eileen O'Connor, a former Assistant Attorney General, United States Department of Justice Tax Division; and Jonathan Turley, a professor of law at George Washington University and a Fox News contributor.
Democrats will hear from Michael Gerhardt, a constitutional law professor at the University of North Carolina. Gerhardt served as special counsel to the presiding officer of former President Donald Trump's second impeachment trial.