It's hard to anticipate the potential ramifications of a widespread breakdown in national trust. The lack of faith in the fair transfer of power poses an existential threat to the republic and a critical mass of the populace could take us down dark paths, where the perception of desperate times produces a will for desperate measures.
It doesn't necessarily have to be a direct threat of violence. With sufficient motivation, critical infrastructure serving large swaths of the country can be efficiently sabotaged within a single state or municipality, even more so with that local government's cooperation. Think ports, bottlenecks at bridges or mountain passes, communications, financial services, and power/fuel lines. Disruptions in these areas amounts to an economic siege to attempt to force compliance from the rest of the nation. It's worth considering what resources are at risk of being cut off by other states in protracted conflict and either stock up or find alternatives. We've seen this before when fuel producing nations shut off the pipelines to consuming nations in the middle of winter. As hard as it may be to fathom, we have to consider the prospect that states and large cities could leverage their resources and economies in order to sway a national outcome.
A big unknown is the potential for use of force by the federal government (regardless of which party controls it) against states that go down this path, as well the compliance by individual members of federal agencies in carrying out orders. So, too, state and local governments' ability and will to support or suppress their own populations with national guard, police, or militia forces.
Also, in this type of scenario, controlling the flow of information used to influence public sentiment will be paramount. Foreign actors have already mounted cyber and psychological operations to influence the electoral process, so the motivation to do a better job in the future raises the temptation of over-correcting and throttling the internet and social media in ways that seriously impact the economy, to say nothing of free speech. With so much of our gross national product dependent on the internet, the economy could take a huge hit. How much economic pain the respective sides are willing to absorb in defense of their political beliefs is unknown.
It's tempting to book an extended international vacation until things shake out but, with a US consumed by interregnal strife, the rest of the world may not be much better.
