Author: Ledyard King and Maureen Groppe, USA TODAY

Democrats are trying to convince at least four GOP senators to join them in demanding witnesses in the trial. If they don’t, the trial likely ends.

The oath is administered any time the Senate considers impeachment. Previous trials show lawmakers have used their own judgment to follow its intent.

Former Vice President Joe Biden on Friday called President Donald Trump a “tragedy in two acts” for the way he characterizes people.