I think that total widespread collapse is unlikely. It would more likely be a slow downturn that would end with a vastly poorer country with fewer resources spread between more people. Because the change would happen slowly, widespread instability wouldn't happen.
The scenarios that would cause widespread problems would be ones that displaced people on a larger scale than Katrina did. The Great Depression was an economic failure with an accompanying ecological disaster that forced huge numbers of people to move. Parts of the country became almost uninhabitable due to the Dust Bowl, and food production was down. I think something similar would be needed for the kind of societal breakdowns to occur.
So...drought combined with oil shortages that lead to food not getting to the inner cities. This would food riots in cities and deprivation in rural areas. If prolonged this could cause serious civil unrest. I also think that water may become a factor in any future unrest. Much of the population of the US has shifted to California and the Southwest, which are water poor areas. The water allocations for California growers and California residents are already causing problems and few places have sane water policies in place. If drought limits water to urban areas, and the states with water fight letting their water go to urban centers far away, there could be widespread unrest and social collapse.
The other extreme weather situation is ice age brought on by global warming; which is not an mythological idea. Ice ages happen much faster than other climate changes, and the tipping points happen fast. Fast being something like 100 years; but drier colder weather in the grain belt would cause many problems. The prolonged blizzards that cripple parts of the country for days would cripple them for months and the growing season would shorten and there would be food and fuel shortages.
So my main answer is still nope. I think most changes would be slow enough that it would be the frog in the pot of cold water reaction. I think local instability is possible, Katrina showed us that. But much of the reporting of really bad things happening during Katrina turned out to be false. We did not end up with disease outbreaks and wars in the streets. Blizzards across the country have disrupted areas, but not the entire country. As have earthquakes. So I think it would take a natural disaster of monumental proportions to cause widespread collapse.
Or for a final vision; coordinated terrorist attacks in multiple cities across the US, combined with some nasty computer viruses. Or a deadly, long incubation time biological agent released at something like a bowl game or the world series or a party's national caucus. Something that brings people from all over the country together for a very limited time. They then get on planes and go home to spread whatever. A two week incubation period would get the whatever all over the country, and if the initial symtoms were mild and cold like it would continue to be spread even after people got sick. If the biological agent was sufficiently dibilitating and contagious, it wouldn't even have to be deadly. Making large numbers of people too sick to work for months would do it. Something like a more contagious and nastier version of mono would do it. A national caucus would be a particularly nice touch since it would take out the government as well.