Who are the only people allowed to order government buildings to fly their flag at half staff?

In the United States, the authority to order flags to be flown at half-staff is typically reserved for the President, state governors, and local officials. The President may issue such orders for federal buildings, while governors can do so for state and local government buildings. Additionally, certain statutes and protocols dictate half-staff observances for specific occasions, such as mourning the death of prominent individuals.