IT IS noon on a Wednesday so around 40 of Keith Rothfus’s constituents have gathered, as they do every week, outside the Republican congressman’s office in a northern suburb of Pittsburgh. Despite a light drizzle, they are in high spirits. Many wave stars-and-stripes flags or brandish placards daubed with slogans protesting against Donald Trump and Mr Rothfus, including especially the congressman’s weak-kneed refusal to meet them at a public event. “Investigate Russiagate!” reads one, “Real News, Fake President!” another. “Uncle Sam wants health care for all!” reads Carolyn Gibbs’s placard. A statistical analyst, who works for a commodities trader, the 55-year-old is wearing the Uncle Sam costume her teenage daughter bought for Halloween. “It’s important to me that our protest is joyful and expresses our patriotism,” she says.

Like many attendees at the weekly “Where’s Rothfus? Wednesday” protest, which was launched in February by a group of local women who had met on a bus to the Women’s March—an anti-Trump protest in which perhaps 4m Americans took part—Mrs Gibbs is new to activism. She had not given money to a political campaign until Mr Trump insulted the bereaved parents of a Muslim war hero last July, which persuaded her to give $100 to Hillary Clinton. “It pushed me over the edge,” she says. Besides showing up for “Where’s Rothfus?” she also hosts her own “Potluck for Perseverance” evenings, which she describes as occasions for “like-minded moderates and progressives” to meet, discuss issues and pen badgering letters to Republican lawmakers.

This snapshot of leftist protest might have been taken in almost any of America’s 435 congressional districts. The energies unleashed by the Women’s March, the biggest political protest in American history, have been sustained. In even the most conservative places, including the lily-white northern suburbs of Pittsburgh, where Mr Rothfus won in November with a big majority, established centre-left groups report massive increases in support and new ones are mushrooming. MoveOn, an online protest outfit with 8m members, says it has three times as many monthly donors as it had before Mr Trump’s inauguration. “This is what we were made for,” enthuses its director in Washington, DC, Ben Wikler. Primed by social media, and fuelled by ever-rising outrage at Mr Trump, the most successful new entrants are growing even faster.

Liberty and justice for all

Pantsuit Nation, a pro-Clinton Facebook group started during the election campaign, had 3m members by the end of it. A report by the Centre for American Progress, a think-tank, reckons 140 new groups have been launched since then. The breakout star of the new activists, Indivisible, was launched by a pair of former Democratic congressional staffers in January, and now has 6,000 groups, in every congressional district, including 15 in Mr Rothfus’s.

Indivisible followers swamp their local Republican lawmaker with pestering letters, jam their phone lines with inquiries, about their votes or intentions to vote, buttonhole them in public and organise protests rallies when they go to ground, as many now have. “Where’s Rothfus?” is an example of this. A sister protest, “Tuesdays with Toomey”, named for Pennsylvania’s Republican senator, Pat Toomey, draws several hundred protesters to his offices in Pittsburgh and Philadelphia every week.

“America has a representative democracy and all members of Congress, whether good or bad, mainly want to get re-elected,” says Ezra Levin, one of Indivisible’s founders. “This makes local constituents very powerful.” The organisation has also been prominent in rallying Democrats in a series of special elections, in Kansas, Montana and Georgia, to replace congressmen hired by Mr Trump’s administration. In formerly safe Republican districts, these contests have seen outsized Democratic turnouts and surprisingly stiff competition. A run-off vote on June 20th for the Georgia district, which was vacated by Mr Trump’s health-care secretary, Tom Price, could give the Democrats their first major electoral victory since the general election. If so, Indivisible, which has 19 groups in the district, will take much of the credit.

That would also encourage many charged-up progressives to believe they could overturn the Republicans’ 45-seat House majority in the mid-term elections due next year. That would represent a stunning reversal for the Republicans; it could even lead to Mr Trump being impeached. Yet even as things stand the new progressive activism looks likely to have major consequences for both parties—and perhaps even for the nature of parties.

A comparison with the Tea Party, a conservative grassroots reaction to Barack Obama’s election and economic stimulus policies, helps illustrate that. Its activists pioneered many of the confrontational tactics Indivisible has adopted. “If you subtract the racism and negative values, the Tea Party had a really smart strategy,” says Mr Levin. Yet at its height the Tea Party consisted of only about 650 groups, whose members were predominantly middle-class, middle-aged white men. Though undeniably a grassroots movement, the Tea Party also depended on support from established libertarian moneybags, such as FreedomWorks, an enterprise of the industrialists Charles and David Koch. Setting aside its role in preparing the ground for Mr Trump’s angry insurgency, the Tea Party’s enduring achievement was to create a caucus of around 40 obstructive Republican House members, which has plagued Republican congressional leaders ever since.

By contrast, Indivisible alone appears to have a much greater potential to promote its members’ preferred issues and candidates and in turn affect the course of many more elections than the Tea Party did. Given also that the Democrats are at a historically low ebb, obliterated electorally in much of the country, and with institutions badly neglected under Mr Obama, groups such as Indivisible might not merely influence the party, as the Tea Party influenced the Republicans. They could even obviate it.

That might appear to be Indivisible’s plan. It recently launched an electoral arm, which among other things will help recruit and promote the sorts of progressive candidates its founders and many local group members admire. It also plans to start endorsing candidates in Democratic primaries; and perhaps launch primary challenges to Democratic incumbents who are considered insufficiently left-wing or trenchant in their resistance to Mr Trump. Indivisible members in New York gave Chuck Schumer, the Democratic leader in the Senate, an early taste of their disapproval, by noisily protesting against his votes to confirm several of Mr Trump’s first cabinet nominees; he voted against the rest. “Half the battle is making sure Democrats have spines,” says Mr Levin.

The obvious risk is that the Democrats, gifted a fine opportunity by Mr Trump to recover their lost ground, are about to be dragged into the sort of left-wing purity contest that would send moderate voters packing. Indeed, there are signs that this is already happening. Heath Mello, a charismatic 37-year-old Democrat, recently lost a strong bid to become mayor of Omaha, Nebraska, a state almost entirely in Republican hands, following a damaging intra-Democratic row over his pro-life views.

Yet there are also reasons for the Democrats to hope such tensions can be mitigated. Most newly energised progressives are united, above all, by their detestation of Mr Trump. Otherwise, the protesters in Pittsburgh suggested, they are a more diverse crowd than the earnestly progressive, indefatigably hipsterish, new activist leaders might suggest The organiser of the “Where’s Rothfus?” protest, Linda Bishop, is a retired banker who was until recently a registered Republican. Her colleague Stacey Vernallis, the leader of a group, PA12 For Progress, which is co-ordinating protests against Mr Rothfus, is a retired lawyer and self-described fiscal conservative.

For Democratic politicians vying to appeal to this massive and growing crowd of fired-up progressives, the answer may be to worry less about ideology and more about tone. Democrats, like Republicans before them, are clamouring for a fight. “"We don’t simply need progressive votes in Congress. We need thunderous, righteous champions,” says Mr Wikler. Left-wing purity may be a secondary concern, at least for now.