A day that began with the outgoing president’s pardon of lawmakers and his own family ended with the incoming president’s pardon of supporters who attacked the U.S.

President Joe Biden on Monday issued preemptive pardons for prominent critics of President-elect Donald Trump and members of his own family, using extraordinary executive prerogative as a shield against revenge by his incoming successor.

The extraordinary wave of pardons Monday — from Joe Biden as he left the White House and from Donald Trump as soon as he returned to it — demonstrate the potency of the Constitution’s pardon power, but also expose its perils,