> Practically speaking, when the majority of people who decided to vote voted for the person applying these policies, what mitigations are left?
If its just that, the other branches of government. Of course, Congress is not a remedy at the moment, though its conceivable they might move in response to popular pressure more easily than the White House.
Failing that, history is full of examples of ad hoc remedies where a leader unmistakeably exercised authority in a way which upset people without any formal systemic remedy, some of which took the shape of legal process despite the absence of preexisting formal law, and some of which did not.