Traditional protesting may be a dead end: the GOP will absolutely encourage vigilante violence against anyone they believe is threatening the regime. Given how organized the far right is, and how omnipresent assault weapons are, I could see a massacre rivaling Tianenmen Square happening.

But, for good examples, I'd look at Hong Kong and the Resistance in France during WWII as examples of how individuals can find ways to gum up the works, or thwart fascist governments with civil disobedience, or using internal corruption and lack of oversight against them.

A fascist American government will do horrible things. It's up to the good people to be willing to break the law to mitigate them (e.g. stamping passports for people who theoretically aren't allowed to escape)