> The centre is the bulk that moves. It's the part that decides.

No, it isn't. That's exactly the problem. Trump found a bug in the system, a security hole, in the form of leveraging the non-linearity built in to the current system. The Constitution was designed to produce minority rule, on the assumption that if the minority abused that power too much the majority would rise up and force them out of power. The problem is that this bias is amplified by modern communications technologies, which allow a determined person to leverage a fairly small minority into effective dictatorial power. The Constitutional bias towards minority rule is amplified by party politics, gerrymandering, echo chambers, etc. to the point where you only need a few million motivated followers to effectively control the agenda. All you need is enough voters following you that you can pose a credible threat to unseat any politician in your party at the next primary. Those few million motivated followers are much more likely to be found at the extremes than in the center, and they are much more likely to be found in rural areas and hence be conservative. Given enough time, this influence can be leveraged into enough disenfranchisement through legitimate-seeming voter suppression efforts that unseating the minority becomes effectively impossible through any legal means. At that point, the minority no longer needs to compromise. And since it is the most radical members of the minority who are the foundation of this strategy, the result is extreme radicalization. And all this can happen without moving the center. That's the problem.