Based on the idea that the all these groups still cares about the Constitution, democracy, and freedom.
Why would the military disregard the Constitution and start killing all the members of Congress just because Trump order them to? Though the military take orders from the President, the military has to uphold the Constitution. The President can't just order the military to disband Congress. The military would never do that. What would actually happen is that the military will instead arrest Trump and Congress will put Trump to trail to impeach him.
Again, the scenario where Trump become a dictator of the United States is never going to happen, because there is just too many groups and too much opposition to him.
There is no way the military will kill their own family members just to satisfy Trump's order.
Cops are NOT under the control of the federal government. Cops are under the control of the 50 states. Why would the 50 states give control of the police force to the President? Why would the 50 states just sit back and let Trump become a tyranny without fighting back? Why would cops go against their own cities, just so Trump can become a dictator?
Why would armed people joined up with Trump, especially arms Black people?
Why would the National Guard, who's duty is to protect the country, why would they go against the country just so Trump can become a dictator?
Again. Never gonna happen. There are too many groups who value democracy and freedom. And they will all oppose Trump if Trump decides to do something unconstitutional.
And you seem to be under the assumption that Trump supporters want a dictatorship. That's ridiculous. Trump supporters do not support a dictatorship. Trump supporters supports conservatism (aka, less government), which is the opposite of a dictatorship (total government control).
ALSO: Minutemen was just an example. Now-a-day, it's the NRA and other militia groups. And Minutemen actually refers to these: https://en.wikipedia.org/wiki/Minutemen
Obviously, all these doesn't matter if everyone in the United States (that means, all the people, Congress, judges, police forces, etc. everyone) agrees that Trump should be a dictator and voted to turn the government into a dictator. But that's never gonna happen. People come from other countries into the United States because of its democracy. Why would they allow the government to turn into the same dictatorship they ran away from?