Those who support and/or actively engage with violent, regressive liberal hate groups such as antifa or any other groups you see lately on the news assaulting innocent people, destroying public/private property, etc.
They're well known for instantly resorting to violence for something as simple as disagreeing with them politically.
I also love how people are pretending this is just some conservative boogeyman. Like people were unable to turn on the TV and see these people assaulting innocent people, destroying a local Starbucks, and setting fire to a vehicle during the president's inauguration. Violent liberal extremists aren't exactly known for their sublety