Why U.S. Flags Are Being Flown at Half-Staff on Inauguration Day—And Trump’s Reaction

 https://time.com/7204711/us-flags-flown-half-staff-inauguration-day-trump-reaction/

The act is in accordance with a proclamation issued by President Dwight D. Eisenhower in 1954, which states that when a President or former President dies, 30 days is the appropriate amount of time to fly the flag at half-staff at federal government buildings and their grounds, as well as at U.S. embassies and other facilities abroad, including military installations and vessels.