It might go something like this:
1. Trump loses
2. He declares the election illegitimate and suggests he won't leave
3. People turn out to protest his defiance.
4. Trump's Q and white nationalist disciples turn out to stir the protests into violence
5. The violence escalates to levels never seen before as many of the police take the side of right wing extremists. Violence may even degrade to vigilantism by right wing extremist executions of liberal agitators. Liberals may try to fight back, but are not nearly as well armed
6. Trump declares martial law and sends in Federal officers, and perhaps willing military personnel, to squelch the violence and round up "agitators"
7. As #6 only causes more violence, Trump declares that he may not be removed from power until the crisis is averted.
8. ?????? Depends on what action our military decides to support, and whether the military stays united.
9. We could end up with a long-term civil war.
I'm sure this could go a lot of different ways... I hope it simply goes with a peaceful transition of power. But this country is tiptoeing around on broken glass right now. It's not going to take much for a lot of blood to flow.