I expect that it will take "only" 10-15 years. It won't look like what we think of as a civil war either.
A failure of Medicare/Medicaid due to insolvency is 3-4 years away. A cascade of failures to State pension plans in Illinois, California, and Pennsylvania should occur in the 2024-2028 time frame. Other States will follow.
Of course the Federal Government will bail out these programs. The checks (or EFT deposits) will keep on coming no matter what. Except for a few minor delays, and that one time or two when the amounts were shorted. But the Government promises to make good on those payments. Eventually.
Inflation, price controls, service interruptions, shortages, enforcement of the new anti-hoarding laws, and selected tax increases will do more harm than riots or revolts. We will get those too as things wear on. But people will adapt to increasingly totalitarian Government rules with disheartening speed. People will in fact clamor for more authoritarian rules after a few spectacular terrorist events.
What people cannot adapt to is extended failures of water, sewer, and electric power systems in a metropolitan area. Suppliers that do not get paid stop supplying and technicians who cannot afford transportation to get to work stop maintaining complex systems. Those systems fail. Service gets restored. Then systems fail again. The intervals of downtime get longer and longer. People in the affected areas get very agitated. There are protests which turn into riots. The Police, and later the Army manage to suppress them. Until the next time.
Such things are highly localized. If you are 50 miles away from the latest disturbance, life goes on as if everything is still normal. Everybody keeps pretending. You are not affected, until the rolling problems finally hit your town.
Politicians make new laws and emergency decrees which are contradictory, unenforceable, and quite simply insane. Bureaucrats and Police charged with execution of these policies simply give up and hide in their offices, rather than face an increasingly hostile public.
Most serious violence will start with Government-sponsored militia such as the Antifa franchises. The professional organizer funding for these groups comes from a complex web of "Non-Profit Organizations", which often track directly back to tax-payer sources. As things get tight, the factional disputes over money will get ugly. Leftists will solve these disputes by force.
Leftists are fondly imagining that they can hunt down the Deplorables and destroy them. But people that can actually do that sort of thing will not feel restrained from turning on their own colleagues over internal disputes. And they will. This will weaken them until they cannot sustain enough force to resist external opponents.
Organized criminal gangs, operating strictly for profit motives are likely to do much better than ideologically-based Leftist groups. If they are smart enough to protect the people who keep the freighter, water, sewer, and power systems running, they will become the core of the new Government.
"Interesting Times".