Some Conservatives would say “when an unpalatable and anti-Constitution candidate wins”. This Conservative says never.
We play the game by the rules set in the Constitution. When and if they try to change the rules of the game without amending the Constitution, THEN we restore the Constitution. Until then our foes (and our “friends”) have walked on, but not attempted to throw out, the Constitution.
The present administration has been one of the worst as far as adherence to Constitutional principles, yet how many of us yearn for a military coup? How many military coups in history have instituted anything other than a military dictatorship?
And the Constitution includes the Second Amendment, specifically enumerated, for a reason:
"....that whenever any Form of Government becomes destructive to these Ends, it is the Right of the People to alter or to abolish it, and to institute new Government...." - Thomas Jefferson
Don't argue with me, argue with TJ.
I will make a comparison to Rome. The Republic was ended after they attempted to bring Julius Caesar up on charges. Caesar brought his army with him from Gaul. After the Senate assassinated him, his nephew Octavian secured the backing of the army, then purged his political opponents from power.
I can easily see our current republic ending in a similar scenario. I once spoke of this to some one who was rather liberal and a history buff, his response was "Petraous as Caesar?".