This seems to have been an attack on Republican congressmen, rather than an assassination attempt on any particular individual. If the shooter didn't know what team was practicing, he wouldn't know who was actually on the field at the time.

Given Sanders' comment about the shooter having been a volunteer, one could assume that Democratic congressmen would not have been fired upon, but that remains uncertain.

I'm glad there were no fatalities other than the shooter, but I wonder if this is not the start of a decidedly more disturbing and dangerous phase in the polarization and increasing hostility between US ideological and partisan camps.