Such cascades explain how huge political upheavals can quickly emerge, seemingly out of nowhere. Examples include the revolutions that swept Europe in 1848, the sudden collapse of communism in 1989 and the Arab Spring of 2011.

Now, nothing says that such cascades have to be positive either in their motivations or in their results. The period 2016-17 clearly represented a sort of Alt-Right Spring — springtime for fascists? — in which white supremacists and anti-Semites were emboldened not just by Donald Trump’s election but by the evidence that there were more like-minded people than anyone realized, both in the U.S. and Europe. Meanwhile, historians have described 1848 as a turning point where history somehow failed to turn: At the end of the day the old, corrupt regimes were still standing.

I nevertheless find the surge of indignation now building in America hugely encouraging. And yes, I think it’s all one surge. The #MeToo movement, the refusal to shrug off the Parkland massacre, the new political activism of outraged citizens (many of them women) all stem from a common perception: namely, that it’s not just about ideology, but that far too much power rests in the hands of men who are simply bad people.

And Exhibit A for that proposition is, of course, the tweeter in chief himself.

At the same time, what strikes me about the reaction to this growing backlash is not just its vileness, but its lameness. Trump’s response to Parkland — let’s arm teachers! — wasn’t just stupid, it was cowardly, an attempt to duck the issue, and I think many people realized that. Or consider how the Missouri G.O.P. has responded to the indictment of Gov. Eric Greitens, accused of trying to blackmail his lover with nude photos: by blaming … George Soros. I am not making this up.

Or consider the growing wildness of speeches by right-wing luminaries like Wayne LaPierre of the N.R.A. They’ve pretty much given up on making any substantive case for their ideas in favor of rants about socialists trying to take away your freedom. It’s scary stuff, but it’s also kind of whiny; it’s what people sound like when they know they’re losing the argument.

Again, there’s no guarantee that the forces of decency will win. In particular, the U.S. electoral system is in effect rigged in favor of Republicans, so Democrats will need to win the popular vote by something like seven percentage points to take the House. But we’re seeing a real uprising here, and there’s every reason to hope that change is coming.