This scenario is indeed plausible. Something we would not have thought of a decade ago.

In Canada, the Conservative Party is electing a new leader. The front runner is not a moderate. The moderate Liberal Party (now in power) will eventually do some silly things to cause it to lose the election.

The only saving grace is that Deep Blue vs. Deep Red often implies a 60/40 split. So the the communities are not as divided as much as the analysists portray them to be be. But if one side is making most of the noise . . . . . .

In Chapter 7 of my book, I talk about how an oligarchy can move towards my alternative democracy. I was using the oligarchy that is common with many African nations, where significant suppresion of rights is necessary to hold civil order. But I think Chapter 7 needs to have an addendum to include builing this new democracy within the rule of several oligarchies within the USA.