“They” wouldn’t be letting anything go unless he won a fight.
But that also depends on how you define “fight”, and those who oppose Trump have really struggled with that in trying to defeat him.
Look: fascism is soooo effective in undermining functional democracy because it, like, breaks democracy. Like, if democracy were a rules and bureaucracy machine that did good government (ideally), fascism works by identifying and exploiting its weak points in a systematic fashion. Mass media, systemic bureaucratics, advanced administration, logistics— all of this is ripe for disruption and takeover. And, unlike democracy, which functions on strict rules and ethics and is, thusly, slow to respond to attacks, fasism (esp neo- and ur-fascism) attacks from the outside at weak points rapidly with great agility, following few rules that encumber it.