For only the third time in US history, an impeachment trial is under way in Washington. President Donald Trump is accused of an abuse of power and obstructing Congress.
Many believe it’s a foregone conclusion that Mr Trump – who denies the charges – will be acquitted at the end of this process because his party controls the Senate.
The BBC’s Anthony Zurcher explains how events could yet diverge from the script.
Video by Maxine Collins and Chloe Kim