Political violence is wielded against dissidents in the United States constantly. Another way to think of this is that a government that resorts to political violence against its own citizens is not a democracy.
Yes, exactly. One of the definitions of a State is that it's the organization holding the monopoly on legitimate use of violence.
When a State becomes undemocratic, it can more easily wield that violence against its own people. Part of the founding ideals of the US is the hope that the people would oust such a State, explicitly through the threat and application of violence if necessary, thus the second amendment.
