Well things are pretty violent already, with the deadly class war the police is fighting against the population (~1k in 2017, https://www.washingtonpost.com/graphics/national/police-shoo...) plus the countless arrests, macing, tasering and other violent actions of police against peaceful demonstrators, plus all the violence committed by Nazis (e.g. the Heather Heyer murder and the other actions counted as right-wing domestic terrorism). Add in the huge number of weapons circulating in the US... when the poor people (or the armed rednecks) finally feel desperate enough that will be quite a bloodbath.