Last April, working the rope line after a campaign visit to Pittsburgh, Hillary Clinton stretched out her hand to greet Yong Jung Cho. The Democratic presidential candidate was walking into a familiar ambush — a shouted question from a climate change activist, with a camera set to record.

“Will you reject money from registered fracking lobbyists?” asked Cho, who was working with the anti-fracking group 350 Action.

Clinton laughed. “Go read the articles!” she said. “I’ve debunked all of that.”

Clinton went on to win the Pennsylvania primary, and the Democratic nomination, and Cho went on to co-found We Will Replace You, a new PAC that’s warning Democrats of primary challenges if they don’t fight President Trump everywhere they can. Among the group’s demands: opposing “all Trump appointees” and “all of Trump’s legislative priorities”; “sing Congressional processes and rules of order to systematically bring all business to a crawl”; and “publicly supporting impeachment if Trump is found to have broken the law or violated the Constitution.”

“We were not happy to see some Democrats vote for so many of Trump’s appointees,” said Claire Sandberg, a co-founder of the group and the digital organizing director for Sen. Bernie Sanders’s (I-Vt.) 2016 presidential bid. “Seeing two Democratic senators vote for Rex Tillerson was absolutely appalling. Seeing 14 vote for Mike Pompeo was absolutely appalling. It seemed that Democrats in Congress were not getting the message,” Sandberg said, referring to Trump’s secretary of state and CIA chief.

“And since then, we’ve seen [Sens.] Jon Tester, Claire McCaskill and Dick Durbin express the opinion that Neil Gorsuch deserves a fair shake, after Republicans refused to do that much for Merrick Garland,” she said in comparing Senate treatment of Trump’s and former president Barack Obama’s Supreme Court nominees.

We Will Replace You is the latest of several projects designed to warn Democrats of consequences in their primaries — or in 2018’s general elections — if they make deals with Trump. Justice Democrats, launched last month by progressive commentator Cenk Uygur, issued a detailed progressive platform and hinted at primary challenges if Democrats ignored it. Last week, a small crew of Sanders campaign veterans launched Draft Bernie for a People’s Party, arguing that progressives needed to give up on the Democrats altogether and break the two-party system.

“Even the most progressive candidates for DNC chair do not oppose large campaign contributions to party politicians from billionaires and super PACs,” Draft Bernie co-founder Nick Brana wrote in a Huffington Post op-ed. “How can we free our government from the influence of the oligarchs without even challenging their mechanisms of political control? Our country was much more sharply divided over slavery than it is over present-day money in politics and inequality. Yet Lincoln’s Republicans replaced the Whig Party in four years.”

We Will Replace You, like Sanders himself, is more focused on changing the Democrats. In addition to 350 Action’s Cho, the PAC’s co-founders include 350 Action Executive Director May Boeve, Sanders’s 2016 digital director Kenneth Pennington, former U.S. Student Association president Alexandra Flores-Quilty and Communications Workers of America National Political Director Rafael Navar. The activists’ experience, Sandberg said, suggested that they could apply pressure on Democrats whether or not they were raising funds to challenge them.

“The most effective thing you can do to persuade voters is mobilize volunteers to talk to them one-on-one, door to door,” Sandberg said. “That doesn’t cost much money.”

Still, the recent record of progressive primary challenges is mixed, with some victories in House primaries but high-profile losses in Senate races.

In 2006, the last year that Democrats took back Congress from Republicans, some left-wing energy was directed at a successful primary challenge of Sen. Joseph I. Lieberman (I-Conn.), a supporter of the war in Iraq. Lieberman went on to win reelection as an independent. In 2010, the Progressive Change Campaign Committee waged a near-miss primary fight against Sen. Blanche Lincoln (D-Ark.); Lincoln went on to lose reelection by a landslide.

So far in 2017, said PCCC co-founder Adam Green, the group has not talked to potential primary challengers of red state Democrats. It has, however, polled possible messaging against Trump nominees, to prove to wavering Democrats that they’d be in better shape politically if they cast “no” votes.

In one poll, the PCCC asked voters how they’d feel about now-Secretary of the Treasury Stephen Mnuchin if they learned that he’d “submitted inaccurate information to the U.S. Senate, and hid $100 million of his wealth from the committee charged with approving or denying his nomination.” In Ohio, Wisconsin, and Florida, close to 70 percent of voters said they’d oppose him.

“Right now, in some states, we’ve found that voters think Trump is taking on special interests and Democrats are defending them,” said Green. “I’ll just quote something P.T. Barnum said — if you want people to look at what you’re doing, start a fight.”

Sen. Chris Van Hollen (D-Md.), the chairman of the Democratic Senatorial Campaign Committee, noted that fewer senators were voting to approve Trump nominees, and he said he was confident that would-be challengers would come to see the good that incumbents were doing.

“They’re going to recognize that when you’ve got a senator whose values are in the right place, and is also popular in their state, it’s a good thing,” Van Hollen said. “I think the people will recognize the importance of senators who stand up for their states and also embody the right values.”

But Sandberg argued that Democrats were relying on outdated ideas about politics when they insisted that the party’s red-state senators needed to cut deals with Trump.

“We question the underlying assumption that Democrats need to move to the right or make concessions to Trump in order to beat him,” Sandberg said. “In many places where Trump won by double digits, Obama had won by double digits, and Bernie did very well in the primary.”