I may be wrong, but many if not all political assassinations in the US are perpetrated by leftists/Democrats.
In the 1960-70s there was a long string of political assinations in Chicago, mostly wards 26, 27, 28, 31 on the near west/NW side. They were always by the machine/establishment against those challenging the machine. It might be said that those in power were protecting what was theirs.
It would be interesting to see how many national events are motivated by the powerful feeling their power is threatened.