One characteristic common to fascist regimes is the tendency for supporters to assert that their loyalty to the leader is stronger than others', through ever more extreme displays and acts of devotion. Leaders pit underlings against each other to construct systems of divide and rule by appealing to their sense of loyalty as well as their overriding ambitions for themselves. Consequently, such regimes are viciously competitive and inherently unstable. Individuals feel driven to constantly monitor their own and others' behaviours and compete against one another to demonstrate loyalty by extremism. Given time this can have disastrous consequences. An example.
The Wannsee Conference that initiated the Holocaust (what the Nazis termed the Final Solution to the Jewish Question) was held in January 1942, nine years after Hitler's rise to power in Germany. Significantly, Hitler was never present at the conference itself. He didn't have to be. The momentum behind the conference was driven by Hitler's underlings competing for his attention and favour by trying to outdo each other in acts of extremism. Convened by Reinhard Heydrich its attendees were below the level of Hitler's inner circle, but who were competing ruthlessly among one another to be elevated to that circle. This competition began in the early days, with Goering, Himmler, Rohm and spread throughout the NSDAP and then the higher echelons of the German government after 1933. Hitler didn't have to do much himself other than to put his cronies in place, set them against each other, and let them get on with the job, occasionally intervening to switch direction - such as when he had Rohm murdered and the SA disbanded. But it began, and was carried forward, by millions of small acts of extremism, each accumulating to give space to bigger and more serious acts, that ended with the destruction of the majority of the European continent.
Few if anyone in Germany in 1933, probably not even Hitler himself, had any inkling at that time that the Holocaust would occur ten years later. In 1933 many Germans thought that the Nazis were rather a joke - a serious and bad joke, but a joke nonetheless - and that their participation in government would be temporary. But they would be proved to be wrong, at the cost of tens of millions of lives.
It takes a long time to take a country to the brink and then beyond it. There are many opportunities along the way for citizens to stop these movements in their tracks and go in another direction. Each individual act either adds to or takes away from the accumulation of acts necessary for these regimes to achieve their worst. And it's not hard to see signs of the potential for a renewed fascism - or something like it - to erupt again, either in the UK or USA at present, but in other places too.
Everyone is responsible for protecting society from fanaticism and extremism. The place to start is to call out those acts that lead in the wrong direction, and to discuss with our fellow citizens what we think is acceptable and where we want our country to go in future. History never repeats itself exactly, so to dismiss the lessons of history on the basis of differences in context is to misunderstand its meaning. And nothing is inevitable. But we need to be reminded occasionally, lest complacency or weakness allow these people to exploit the cracks in our delicate democracies.