President-elect Donald Trump has expressed frustration that flags will be flying at half-staff when he takes office later this month.

It’s an action put in place by President Joe Biden to honor the late President Jimmy Carter, who died Sunday at 100. It’s not a timeline that Trump can do anything about — until after he takes office.

Here’s what to know about why flags are lowered when a president dies, who can issue that order and how long the process lasts: