The use of the autopen, a device that reproduces signatures and is ubiquitous in government and business, is ordinarily uncontroversial. There is no power to undo a pardon in the Constitution or case law.

A 2005 memo from the Justice Department, issued during George W. Bush’s presidency, said that using an autopen to sign official documents is legal, and the practice is now widely used.

Donald Trump says Joe Biden's last-minutes pardons via autopen are null and void. But what is an autopen? And what does it mean for pardons?