It’s now been six dizzying and nauseating months since Donald Trump took the oath of office, and the brightest spot on the American political landscape is the grassroots resistance that has sprung up to counter his regime. No previous president ever faced so many protests so early in his term, and the millions who have taken to the streets since January can already take significant credit for stalling and frustrating key aspects of Trump’s agenda, from his Muslim ban to his bid to repeal the Affordable Care Act. There are numerous qualities that distinguish this organizing upsurge from past waves...