What could easily happen much sooner than 5 years is an incident that gives Trump an excuse to invoke the Insurrection Act, and send federal troops - not just National Guard - into blue US cities. Things could go a lot of different ways after that, but something resembling civil war - or a smaller-scale guerilla war - is very much in the realm of possibility.

Be wary of normalcy bias, it's a big part of what lets the Trump admin get away with what its doing. People think "oh that can't happen"... until it does.