If the U.S. were no longer generally recognized as a democracy, it would put the lie to the country’s international claim to be the defender of democratic values. This would presumably not trouble Trump’s supporters, who are loudly stating their intention to withdraw from NATO and support Vladimir Putin’s wars of conquest.
But even more worryingly, the degradation of the U.S. into the non-democratic sort of republic would invite endemic violence and chaos here at home. People do not like having their vote taken away, as a general rule. Already there has been somewhat of a rise in political violence in the U.S., with scattered right-wing terrorism, some rioting in the summer of 2020, and Right-Left street battles that uncomfortably recall the Weimar Republic. So far, assassinations haven’t figured prominently as in the 1960s and 70s, but there was recently one plot to assassinate a Supreme Court justice. If the vote is taken away, it’s not unrealistic to think that the U.S. would suffer an equivalent of Ireland’s Troubles, Italy’s Years of Lead, or worse.
The worst-case scenario, of course, would be a full-scale civil war. The most likely trigger for this would be a disputed Presidential election, in which opposing factions of the U.S. Military backed two rival claimants to the presidency. So far, the military has resolutely avoided even the slightest appearance of dissension in the ranks, but in the case of a disputed election in which both sides had a somewhat plausible legal claim to victory, this might change. This might seem like a tail risk, but a plurality of Americans did tell a Zogby poll in 2021 that they thought a civil war is likely. And essentially ever major media outlet has envisioned a scenario of the type I just described. So this is far from idle or irresponsible speculation.
One thing I don’t think is really possible, however, is a “national divorce”, in which red and blue states go their separate ways.