Political violence? look to the left:

‘Over the last year, we have seen absurd efforts to blame violent acts committed by people who had nothing to do with politics on politicians and activists who have nothing to do with violence. No matter: it is all about political opportunism.
In fact, however, we do have a political or quasi-political movement in the United States that in recent years has often resorted to violence: the union movement. To cite just one example, one of the terrible, little-known outrages of our modern history was the 1990 Greyhound bus strike, when union snipers fired on Greyhound buses across the country. There were at least 21 such incidents, in some of which passengers were shot. Union leaders, to my knowledge, were never punished for the armed guerrilla attacks they organized…’      Powerline blog