They gain strength by exploiting racism, fear, and concerns about economic collapse, on the part of the struggling working class; real and imaginary enemies and scapegoats are central to their far-right political argument.
They have their own media outlets dedicated to spewing their propaganda; energetic and repeated lies are central to getting their program across.
Behind the scenes they get their strength from the pillars of the right: big business and industry, and particularly the military and defense contractors; and of course hate groups.
Aggressive militarism is key to their foreign policy; their domestic policy is marked by cultural warfare, and by repeated efforts to remove constitutional controls on action by the government.
In power, corruption is epidemic among the leaders.
They use a wide range of sledgehammer political tactics, to include sending goon squads to intimidate political enemies, disruption to prevent real debate of political issues, and violence when necessary; they organize quickly into local groups directed to use these tactics to maximum effect. Ironically these tactics increase the fear that they feed on. Eventually these groups get to be so out of control that even the bigwigs who launched the groups are afraid of them – but they can’t stop them.
Actually, this is a profile of the Nazi party in 1930s Germany. If America's wingnuts of today are not brought under control, where do you think our democracy is headed?
As I said earlier, once goon squads realize they can use the threat of violence and disruption to stop the process of political debate, then democracy is dead.