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.
Byzantium kinda had its ups and downs, but unlike the us, it was facing the slow grind of encroaching enemies. Even then, it wasn't until the fourth crusade that things collapsed. After that it was pretty much on life support, but still had its moments. These things about empires spending centuries in declines are more a narrative rather than an accurate reflection of history. It's true collapses rarely happen overnight - more like over decades, until the situation reaches a percolation point, and after that it's years or months...