The "peripheral" countries mentioned in the GP were nations or at the very least distinct semi-national entities before the USSR.

States in the USA have no effective history before being a part of the USA.

I do not think it will happen but this is why in discussions about this happening, or historical fiction, typically the places that break off are the ones that were distinct _before_ they joined the US. Any of the 13 colonies, New England as a block having the strongest colonial identity that I'm aware of, Texas, or California generally are where it's assumed to start as those were countries/had identities very much outside of the US while also having economies that might be ok.

Wrong, Hawaii and New Mexico ( which included parts of Arizona, Colorado and Texas) do

That's fair (I live in NM).

But I would still say that the status of lower-48 states is quite different than, say, Belarus and the USSR.

Yes, Nuevo Mexico existed prior to becoming part of the US, but most of the distinctive identity-forming elements of Nuevo Mexico have been lost or significantly diminished (for a variety of reasons).

I know nothing of Hawaii, the situation there may be similar or very different.

The USSR existed for only about 70 years. There were likely people alive at its creation who were still alive as the eastern European states left it. That's a very different scenario than NM (which effectively entered the US in 1848 with the Treaty of Guadalupe Hidalgo).