Chief Justice Roberts sworn in for impeachment trial

Opening statements in the trial, only the third in U.S. history, are expected on Tuesday (January 21).

As the trial opened, a nonpartisan congressional watchdog on Thursday (January 16) dealt Trump a blow by concluding that the White House violated the law by withholding security aid approved for Ukraine by U.S. lawmakers.

The abuse of power cited by the House included Trump's withholding of $391 million in security aid for Ukraine, a move Democrats have said was aimed at pressuring Kiev into investigating political rival Joe Biden, the president's possible opponent in the Nov. 3 U.S. election.

Trump has denied wrongdoing and has called the impeachment process a sham.