Tens of thousands came to Washington, D.C., for the parade, which was meant to honor the 250th birthday of the U.S. Army, but also happened to fall on Trump's 79th birthday.

In a city notorious for unruly crowds at large sporting events, protesters were peaceful and law-abiding — as were the police.

Detectives don’t yet know why the alleged rifleman pulled out a weapon or ran from the peacekeepers, but they charged him with murder and accused him of creating the dangerous situation that led to A...