There are unstable people on the left, right and in the middle. They can be HS students, veterans, college students, deeply religious, etc.. We do know they tend to always be male. They can be black, white, asian, hispanic. This is why profiling is difficult. This is why I believe that waiting periods, tougher restrictions and mandatory training and testing should be required to purchase a deadly weapon. The second amendment says "well regulated militia" meaning there needs to be some oversight. They understood that.  We can't pin it on political parties but we can look to the environment of the times. There is a lot of divisiveness in our system and that inspires unstable people to act. Both sides need to take blame for this unstable environment, while neither side pulled the trigger they do control the mood of the nation.