Got to 2012 and have a charismatic conservative sweep the republican primaries on a platform of massive deportation, nuclear attack against the country found plotting against us, etc.
The left and their fellow travelers in the media, academia, Hollywood will kick up an outrage, violence will be in the mix. Threats will be made if this conservative is elected against Saint Hillary and if he, or she, wins half the country will refuse to recognize the election.
This scenario is sliding from possible to probable with each passing day.
That's not "one scenario," that's a series of worst-case scenarios, none of which has any necessary connection to the next.
The only "new" thing you've brought to the table is that Hillary Clinton gets elected ... and then what? Would she be effective?