The current issues in the US are a more extreme version of what we've had, which to avoid further comment I'll just call the "EU issue".
The underlying issues are complex, multi-faceted, and have been decades in the making.
A big part of the issue is the disconnect between metropolitan elites and everyone else. In the UK this manifests itself in particular as the Westminster Bubble where the movers and shakers think that London is the centre of the universe and are oblivious to the the fact that the rest of the UK is not the same as London. Someone suggests major infrastructure projects for the London area and no-one bats an eyelid over the costs and planning is sorted out. Suggest infrastructure improvements/needs elsewhere and all of a sudden it's "too costly", "not needed", "can't approve that" etc. A66 upgrade locally being a particular bone of contention.
Politicians in the centre get obsessed with the minutiae of their little world and fail to understand the real needs of the people outside. For a while, perhaps decades, voter inertia and party loyalties prevail and obscure to the centre what is going on. At some point the disconnect leads to a rupture. Some demagogue comes along and tells people they're not listened to and they have a brand of snake oil that will fix everything...
Of course they are liars and charlatans. Unfortunately, for a while it will work unless serious effort is put into countering it.