Dawn had just cracked on America’s 250th birthday when a couple from Texas jogged past a sign outside the U.S. Capitol that read “POLICE LINE — DO NOT CROSS.” It was the start of a day that already wasn’t going according to the organizers’ grandiose plan, but Diane and Bill Riggs, their foreheads beading with sweat, were determined not to let the barriers, physical or meteorological, spoil the occasion.