A county sheriff says more than 20 people were killed, numerous others were injured, though we didn't know the exact the number when we produced today's show.
Emergency and rescue services rushed to the scene. But our reporter says it will take days to clear the track and to establish the numbers of the dead and injured.
Not all casualties can necessarily be prevented — but by coordinating across local, state, and even national borders, officials hope that the worst-case scenario can be averted.
Casualties could fan nationalist flames on either side and cause twitchy officers, or political leaders, to respond in ways that lead rapidly to disaster.