As he marked the solemn 24th anniversary of the Sept. 11 attacks, President Donald Trump announced he’ll posthumously award the Presidential Medal of Freedom to conservative activist Charlie Kirk, who was shot and killed at a Utah college event Wednesday afternoon. In remarks at the Pentagon, Trump expressed "the horror and grief" Americans are feeling at the news of Kirk's killing and he praised Kirk's impact on conservative politics. “Charlie was a giant of his generation, a champion of liberty and an inspiration to millions and millions of people,” Trump said. Kirk, a conservative activist and close ally of Trump who played an influential role in rallying young Republican voters, was shot and killed at a Utah college event in what the governor called a political assassination. The shooter has not been found. Authorities say Kirk was killed with a single shot from a rooftop on Wednesday. Whoever fired the gun then slipped away amid the chaos of screams and students fleeing the Utah Valley University campus. The circumstances of the shooting drew renewed attention to an escalating threat of political violence in the United States that, in the last several years, has cut across the ideological spectrum. The assassination drew bipartisan condemnation, but a national reckoning over ways to prevent political grievances from manifesting as deadly violence seemed elusive.