I have an idea of what the United States will look like in 2020, and it is roughly like the Holy Roman Empire, I'll discuss it more when I post the map of the US in 2020.
That's a rather extreme direction which things would take if we end up with Disunited States. I agree that there is a strong potential for disunity, but as I have also explained quite clearly on the main P&S thread, by 2020 the world will have recovered to a very significant degree and international trade and exchange will again be the order of the day albeit in a more limited form.
If the United States remains as a polity then, I would not be surprised if indeed as you may imply through the HRE comment. That its political structure and constitution is very different from what it was in 1984. Asymetric federalism might be the order of the day, various rights and prerogatives for various states and a much more unequal number of "governmental layers" between various parts and states of the Union.
I bet that a lot of military communication infrastructure has survived in some form, ARPANET structure mades the whole network survivable to a degree. Nevertheless the botched evacuation of Reagan and the mistakes made with regards to the continuity of power will have very severe consequences it seems.