The midterm surge of “outsider” Democratic candidates gets insider scrutiny in the engrossing campaign documentary Knock Down the House.

The operative word in that title is knock. Rachel Lears’ movie follows several progressive women — including, notably, future New York Rep. Alexandria Ocasio-Cortez — as they walk through their districts or states, doing the grunt work of ringing doorbells and shaking hands, hoping to dislodge complacent incumbents in their own party. It’s a mirror image of the Conservative Tea Party uprising of earlier election cycles — and a push toward a more ambitious liberal agenda (Medicare for all, higher minimum wage, student loan relief, etc.).

They’re Democrats, but the movie should be inspiring to anyone who wishes to see firsthand the immeasurable value of good retail politics and hard work.

And how much that hard work is appreciated by voters, seen here as a mostly savvy and pragmatic bunch — in candidate Cori Bush’s Missouri district, and in the Bronx neighborhoods where Ocasio-Cortez runs. There, for instance, voters know that AOC’s opponent, Joe Crowley, is a machine politician who takes money from corporate interests. But they also know the value of an entrenched party loyalist with committee seniority and the benefits that come with it — which is to say, a savory feast of roast pork.

Constituents are blunt: Why should they forgo that and take a flyer on a bartender with zero political experience?

Ocasio-Cortez’s response is part platform (rent, day care, health care, wages), part political talent. There are four women featured here, but the camera plays favorites, and anyone, regardless of political orientation, can instantly see AOC’s unusual gifts. She’s well-versed in issues, yes, but she has the essential (and unfortunately rare) campaigner’s ability to think on her feet. You see her read rooms with an uncanny knack for emphasis and advantage.

Her grassroots, small-donor campaign could be a blueprint for all upstart candidates, but there are national implications, too, for party leaders paying attention. She talks to Trump voters in Queens (part of her district, along with the Bronx), but she doesn’t talk about Trump (and certainly not about Russians). There is a disciplined focus on kitchen table issues important to constituents.

She’s also lucky in her opponent. Crowley has none of her skill and seems almost lazily assured of reelection. He stays mostly in D.C., sends a surrogate to community forums, and, in one particularly telling moment, gives a victory speech in his adversary’s presence, during a debate, several days before the election.

Spoiler alert: AOC wins. Other candidates are not so lucky, but their personal stories are just as interesting, and taken together, they add insight into our nation’s unusual political moment, equal parts instability and possibility.

In a way, Trump and AOC prove the same points: Everyone is vulnerable. But anyone can win.

Knock Down the House. Directed by Rachel Lears. With Alexandria Ocasio-Cortez, Cori Bush, Paula Jean Swearingen, Amy Vilela. Distributed by Netflix.

Run time: 1 hour, 26 mins.

Parents guide: PG (thematic elements, language and brief smoking).

Playing at: Ritz at the Bourse, streaming on Netflix.