If you are unaware, Republican members and lawmakers of the United States were recently the target of a mass shooting in Alexandria, Virginia. It seems that the gunman's target was specifically their political affiliation: he was hoping to kill Republicans.
I find myself noting this as a very strange event, despite the uneasy reality that mass shootings are nearly a monthly event now. Mass murderers of the past seem to have targeted by race, sexual orientation, religion, or government in general (e.g. Timothy McVeigh). There have been, of course, just plain old crazy mass killings with no particular target.
Is this the first time in U.S. history that a mass shooting/killing targeted political affiliation? I would suspect that some of this happened during the Civil War, but that was a war, a very different thing. So outside of military organized action, has there ever been a mass shooting/killing in the United States that targeted a political party?