Byzantium was in decline for seven centuries until the Ottomans pulled the plug. Rome was in decline for several centuries prior to its sacking.
Climate change and the accompanying plagues, droughts, famines, and calamities that accompany it might accelerate and exacerbate the state's capacity and willingness to respond to these crises, but all it might mean is that this is a new normal added to the reproleterization of American life.
I don't really have a point but it is just a thought that I (perhaps others) are going to have to accept that future, and that is a kind of new world I am unsure as to how to adapt to.
There's a pretty good novel called The Parable of the Sower by Octavia Butler
To keep it brief and spoiler free:
The near future US has a populist right wing, mostly ineffective neoliberal government
More fortunate people live in gated communities
Some live in gated company towns
But most of the US is a failed state like Somalia with incredible poverty and violence everywhere