Tom MacArthur’s town-hall meeting should have been uneventful. It was May and MacArthur, a Republican congressman, had come home to New Jersey to talk to constituents, having won re-election with a hefty majority less than a year earlier. Normally, at such an event, he might have expected to field a couple of dozen idiosyncratic questions, trot out some polite replies, wrap up after an hour or so, and go home for an easy night’s sleep.

But it didn’t quite pan out like that.

Six days earlier, the House of Representatives had voted to pass the American Health Care Act, which was predicted to leave millions of Americans without health insurance. MacArthur had written the amendment that had revived the bill, after an earlier version failed to garner enough support. Now, nearly a thousand furious protesters carrying mock-ups of their would-be gravestones were outside the town-hall venue to greet him. The few allowed inside spent five full hours savaging him. “You have been the single greatest threat to my family in the entire world,” one man screamed, in a 10-minute tirade that soon flew around the liberal internet.

This wasn’t a one-off. Republicans have been facing similar outcries across the country this year. Angry protesters cornered Idaho representative Raul Labrador into telling (paywall) a town hall that “no one dies because they don’t have access to health care,” for which he was predictably ridiculed. South Carolina’s Joe Wilson—who memorably shouted “You lie!” at president Barack Obama in a joint session of Congress in 2009—found the accusation chanted back (paywall) at him by constituents. In Utah, Jason Chaffetz received similar treatment and accused attendees of trying to “bully and intimidate” him.

When I asked New Jerseyans at MacArthur’s town hall what made them think to spend their Wednesday evening haranguing their congressman, three words were on most protesters’ lips: “The Indivisible groups.”

The Indivisible Project is the American left’s closest equivalent to the Tea Party, the hard-line conservative movement that crashed on to the political scene in 2009. It was inspired by the Indivisible Guide, a manual written by former Democratic congressional staffers who decoded how to combat Trump’s agenda using protest tactics pioneered by the Tea Party. Following the guide’s advice, activists across the US have bombarded town halls, held sit-ins at lawmakers’ constituencies, and made phone call after phone call to their congressional offices. Their aim is to paralyse the Trump administration by pushing Republican members of Congress to vote against him.

The movement says it has almost 6,000 local chapters throughout the country—at least two in every congressional district—and hundreds of thousands of active members, who run the gamut from socialists who supported Bernie Sanders to Republicans who revile Trump. It’s notched up some impressive grassroots fundraising and claims to have influenced several key decisions—most notably, the vote that killed the Republicans’ flagship policy, the dismantling of Obama’s Affordable Care Act.

And yet, unlike the Tea Party, which immediately grabbed international headlines, the chances are you’ve never heard of the Indivisibles.

That’s a symbol of the obstacles the movement faces. It has two ambitious main goals: to stop Trump from achieving anything, and to transform liberal grassroots activism and the way Americans engage with democracy. Its challenges range from some dissonance between the national leadership and ground-level activists over what the movement is for, to tensions about its ideology, to questions over whether its strategy is sustainable in the medium to long term. Looming above all that is one big, unanswered question: Just how effective is its protest model of lobbying individual members of Congress?

The origins

The Indivisible Project’s founders, married couple Leah Greenberg and Ezra Levin, didn’t think they were starting a mass protest movement. Horrified by Trump’s victory, they decided to channel their experience of being besieged by Tea Party protesters when they were working for members of Congress in Obama’s early years. They cobbled together a wonky 26-page guide and threw it online as a Google document a month after the election, thinking hardly anybody would see it.

“We thought that maybe our friends would read it and that was probably going to be pretty much it, and maybe in six months somebody would let us know that they had read it and we would be super excited,” says Greenberg, a former staffer for ex-Virginia congressman Tom Perriello.

But their Google doc soon started crashing because so many people were trying to look at it, and they were bombarded with messages from people wanting to join an Indivisible group. They encouraged people to start their own groups and began registering them on a website. Within a couple of months Greenberg and Levin had both quit their jobs to head up the new movement full-time.

The theory of change

Since Republicans hold the presidency and both houses of Congress, Greenberg and Levin believe the only option open to anti-Trump activists is to do all they can to block his agenda. That means persuading members of Congress to vote against Trump’s plans by convincing them they won’t get re-elected if they do.

“Donald Trump’s agenda does not depend on Donald Trump,” says Levin, an ex-staffer for Texas congressman Lloyd Doggett. “It depends on whether individual members of Congress choose to go along with that agenda or choose to resist it, and that gives constituents actually a huge amount of power.”

In practice, this largely means educating local Indivisible groups on the Congressional agenda each week and encouraging them to lobby lawmakers—whether Republican or Democrat—to oppose it. Whether or not they succeed on each individual vote, putting up a huge fight can then change the dynamics for other bills, argues Levin, recalling his experience of the Obamacare battle as a congressional aide.

“Although my boss didn’t change his vote, it was clear [the Tea Party] was changing what was politically possible,” he says. “Yes, Dodd-Frank passed, yes, the Affordable Care Act passed, but…we didn’t get card check to support unions, we didn’t get an environmental bill, we didn’t get some of the big job-creating bills that we wanted to see get through.”

In the long term, they hope to have a “progressive infrastructure at the community level,” Greenberg says—in other words, a concrete movement that survives much longer than the Trump administration. The task is to convince a generation of the liberal grassroots that, as Greenberg puts it, “you don’t have to wait for the next election to have a real impact on policy outcomes today.”

What have they achieved?

The Indivisibles’ protest model won its first victory on Jan. 3, the very first day of the new Congress. With Trump not yet president and already mired in questions about conflicts of interest, Republican congressmen inexplicably decided to gut the Congressional Ethics Office. The lawmakers’ offices were soon flooded with angry phone calls and they made a swift and embarrassing U-turn (paywall).

Guy Potucek, who heads an Indivisible group in northern Virginia, says he felt the power of the movement when the American Health Care Act, revamped with MacArthur’s amendment, came up for a House vote in May. His representative, Barbara Comstock, a Republican, was wavering, and Potucek says he assembled a large group outside her office to protest all day. Comstock, an ally of speaker Paul Ryan, eventually voted against the bill, though it squeezed through.

“I firmly believe that had it not been for our constant presence, she would not, for the only time I can think of, have broken with her party on her vote,” says Potucek, 45, whose day job is as an engineer in the defense industry. (At the time, Comstock’s office said she opposed the bill because she disagreed with parts of it, but analysts were quick to point out (paywall) that she was probably trying to curry favor in her increasingly swing district. Then again, she may have done it with party leaders’ approval, since they had enough votes without her.)

More decisive, of course, was the bill’s ultimate defeat in the Senate. Three Republican senators—Susan Collins, Lisa Murkowski, and John McCain—tipped the balance 51-49 against it, and the Indivisibles claimed credit for helping influence all three (though they were also careful, in a subsequent op-ed, to acknowledge other groups that played a part).

Amy Fried, a political scientist at the University of Maine, described the effort to persuade Collins in some detail, and it seemed a perfect illustration of democracy in action: a concerted, civil, and well-argued public pressure campaign in which the politician actually listened and changed. In their op-ed, Greenberg, Levin and fellow co-founder Angel Padilla declared: “The combined political might of the president of the United States, the speaker of the House of Representatives and the Senate majority leader was no match for one simple thing: people showing up.”

So, just how effective is their protest model?

But seen from another angle, the people’s victory against the politicians looks a touch hollow. Trump’s health-care reform was a diabolically unpopular bill about a uniquely emotive issue, with life and death tangibly on the line. The Senate version would have led to an estimated 22 million people losing health insurance within a decade. And yet it failed by only one vote.

That’s the real takeaway, says Theda Skocpol, a Harvard political scientist and author of several books on political activism, including one on the Tea Party. “They voted for it! Most of them voted for it!” she exclaims. “So, clearly protesters and opinion polls and the substance of the legislation weren’t effective with Republicans. There were three: a guy dying of cancer, and two women in states where they needed Democratic voters to win [re-election].” Instead, she says, most Republican lawmakers’ decisions seem to be influenced much more heavily by big rightwing donors and the fear of primary challengers.

Jon Lieber, a former top advisor to Republican Senate leader Mitch McConnell, is similarly skeptical. Most Republicans, he says, have made up their mind to support Trump’s agenda and dismiss protestors as “a bunch of left-wing agitators.” The undecided ones, meanwhile, just use the public opposition as political cover, he says. “With those folks, it probably helps people like Susan Collins when she decides to vote against the ACA bill; it helps her show the public is with her, and she’s getting accolades. But I don’t think it’s influential in making her mind up,” said Lieber, now US practice head at Eurasia Group.

Elected officials’ willingness to write off constituents in favor of donors might explain why the vast majority of Indivisible members are white women, rather than African Americans or Hispanics, says Micah Sifry, a longtime liberal activist and author of several books about politics and protest. “The Indivisible strategy explicitly works best for people who believe that the representative political system should work or still works,” says Sifry, who is a member of an Indivisible group in New York. “If you are past that, [and believe] the political system doesn’t care about me, or actively tries to disenfranchise me, you might not think the Indivisibles’ tactics make much sense.”

Even if the Indivisibles can fairly claim credit for helping defeat the health-care bill, they’re going to struggle to succeed with these tactics in future, Skocpol says. “Any tactic that works early on stops working after a while,” she says. “One of the things social movements have to do is innovate.”

Case in point: The Republicans have grown wise to the town hall protests and simply stopped organizing them. Since successfully persuading his congresswoman over health care, Potucek seems to be feeling this: “We’ve seen very little movement from representative Comstock [since then],” he says.

Is it sustainable?

The right has grassroots evangelical groups; it has the National Rifle Association; it has the Koch brothers’ myriad networks. But that kind of “locally grounded infrastructure has been needed on the progressive side for a long time,” says Marshall Ganz, a sociologist at Harvard who spent 16 years as an organizer for legendary civil rights and labor activist Cesar Chavez.

The Indivisibles want to create that; in fact, Greenberg uses almost the exact same language as Ganz. “Success is long-term, success means developing a foundational progressive infrastructure at the community level,” she says.

But most onlookers can’t imagine the movement lasting if the group keeps focusing its efforts solely on opposing Trump. “It continues to be this emergency, that emergency, another emergency, and people frankly get emergency fatigue,” says Ganz, who has been advising the Indivisibles and is enthusiastic about the movement.

Activists like Caitlynn Moses, the co-leader of an Indivisible group in deeply Republican Arkansas, are already being hit by this. “It’s emotionally exhausting—I don’t think anyone can be here for the long haul in the way we’re doing it now,” says Moses, 23, who juggles her time between activism, studying for a business degree, raising a four-year-old, and working a full-time retail job. “I talked to three members this week who had to step out for a bit because they’re about to have a mental breakdown.”

Moses had never done activism before and has no plans to stop her involvement in politics, but is thinking of eventually moving behind the scenes by starting a Political Action Committee (a fundraising body) to support electoral candidates. Potucek, in Virginia, hadn’t thought that far ahead, and was less certain of whether his group might continue post-Trump: “There are folks who I’ve talked to both in the leadership team [and outside] who have said it would be great when we can get back to our normal lives, so it’s also possible that it just kind of fades away as the immediate threat goes away,” he said.

What are its policies?

There is one way to solidify the movement, boost morale, and grab back the levers of power all at the same time: winning elections. That ranges from the national midterms in 2018, to state and local elections, right down to the school-board level.

The Indivisibles’ leaders are acting on this. They’re currently sketching out a plan for the congressional midterms, which will include endorsing certain candidates, and are going on a “listening tour” to work out their policy platform.

But if that turns out just to be the same policy of opposing Trump, it won’t translate into electoral success, says revered conservative organizer Richard Viguerie. “The British politician Enoch Powell famously said that you need to give the voters a tune they can whistle…Trump did that: ‘Make America Great,’” says Viguerie, who revolutionized campaign tactics from the Nixon era onwards. “The left has not done that. What’s the left’s message? Resistance? No, no, no. I understand their frustrations but that’s not an election scene that’s going to get a lot of victories.”

Marlon Marshall, a top Obama campaign organizer, agrees: “People want to know how government can help them, so we have to articulate what it is you stand for, not just what you stand against.”

The political breadth of the movement’s membership becomes a problem here. Both Moses and Potucek say they try to keep their groups strictly non-partisan in their opposition to Trump so all their members are happy; the national leadership similarly insist they are “not going to act as an arm of the Democratic party.” But the leadership also specifies it’s pushing for a “progressive” message—something Potucek says he’s “struggled with,” since it won’t thrill his Republican members. (Instead, he’s been trying to find common ground on things that trouble members of both parties, like the gerrymandering of voting districts.)

What’s more, once those “progressive” policy demands are defined, there’s a risk that even the movement’s liberal activists will cleave along the lines that have split the Democratic party since the presidential primaries. “We literally cannot say the names Bernie Sanders and Hillary Clinton in any of our groups because people are still so spilt about it,” says Moses.

The next step

Levin is bullish about their chances, nonetheless. Pointing at the series of incredibly close (paywall) special House elections this year in strong Republican districts, he argues the Democrats can take back the House if they come anywhere near that kind of swing in the midterms.

The Indivisibles could help not by backing primary candidates or lobbying Congress, but just by getting anti-Trump voters to turn out in large numbers and vote Democrat, says Skocpol. That, she says, was the Tea Party’s real achievement: Though it gained headlines for barraging members of Congress with criticism, its “upsurge led to people being determined to vote” for the GOP in the 2010 midterms, “even when they were critical of Republicans.”

The Indivisibles are well behind the Tea Party on two matters, though: funding and media exposure. “At this point in the Tea Party trajectory, the Koch brothers, Americans for Prosperity, and Freedomworks had stepped in in a very big way, along with Fox news fanning the Tea Party story,” says Sifry. Liberal icons like MSNBC presenter Rachel Maddow have been vocal Indivisible supporters, but the left doesn’t have a partisan cheerleader with the power of Fox News, he says, while traditional big liberal donors have been holding back, waiting to see which of several groups will become the most prominent. Instead, he argues, “they should be spending like crazy.”

One consequence of this dearth of money? The Indivisibles currently have just eight field organizers for their almost 6,000 local groups—around one organizer per 750 groups. “One organizer per six groups would be more like it,” emails Jonathan Smucker, author of Hegemony How-to: A Roadmap for Radicals.

The long term

Regardless of what political victories they have or haven’t achieved so far, Ganz says the Indivisibles have massive potential because of the stunning breadth of activists they’ve assembled. They reach every single congressional district and in some cases have brought together progressives in areas where they didn’t even know other non-Republicans. That gives them the chance to stand candidates in the scores of districts that Democrats have long abandoned and don’t even campaign in. “[In those areas] people are only hearing one side of story—only the Fox News line,” Ganz says. “This would mean progressives have to talk to non-progressives; that’s kind of important evangelical work to do…you can’t just talk to people who agree with you.”

Indivisible members have already run for office, and more plan to. One has won a city council seat in Iowa; Moses, in Arkansas, says she has members who plan to stand for election at various levels of government. These are small green shoots that, if carefully cultivated, might just grow into something with long-term sway at the local level. That’s crucial for progressives, given the Republicans’ control over 34 of America’s 50 governorships and around two thirds of state legislative chambers. If they can win over a chunk of voters in each deeply Republican House seat, those seats may not turn Democrat, but there might just be a difference in state-wide and national elections.

However, the group’s leaders have a precarious path to tread on the road to their long-term goals. Can they develop a coherent ideology that outlives opposition to Trump? How will they maintain their flimsy coalition of activists ranging from the socialist left to the pro-business right? Will leftist donors step up with the money to let them build a proper nationwide infrastructure? Can they innovate if the Republicans manage to blunt their oppositional tactics?

The jury, on all those questions, is still out.