President Trump has ordered flags to be flown at half-staff across the United States in memory of political activist Charlie Kirk. "As a mark of respect for the memory of Charlie Kirk, [...] I hereby order that the flag of the United States shall be flown at half-staff," the proclamation reads.

State buildings in Missouri will have their flags at half-staff, following the proclamation of Missouri Governor Mike Kehoe. Kehoe posted on X, formerly known as Twitter, that he was “deeply saddened to hear of Charlie Kirk’s passing.”

Congress established Patriot Day shortly after the attacks on Sept. 11, 2001. The observance was signed into law on Dec. 18, 2001.

Sept. 11 is Patriot Day, a day to honor the victims who died in "the deadliest terrorist attacks ever launched" against the U.S.

According to the official website of the U.S. General Services Administration, flags typically fly at half-staff when the country or specific state is in mourning. Observances include national tragedies, days of remembrance and deaths of government or military personnel.