Progressives are threatening primary challenges for Democratic lawmakers who don’t commit to full obstruction of President Trump Donald John TrumpTrump says he doesn't think he could've done more to stop virus spread Conservative activist Lauren Witzke wins GOP Senate primary in Delaware Trump defends claim coronavirus will disappear, citing 'herd mentality' MORE’s agenda.

Democrats already face a daunting 2018 landscape, with 10 senators up for reelection in states that Trump won. However, the threat of primaries foes going up against vulnerable Democrats such as West Virginia’s Joe Manchin Joseph (Joe) ManchinOVERNIGHT ENERGY: House Democrats tee up vote on climate-focused energy bill next week | EPA reappoints controversial leader to air quality advisory committee | Coronavirus creates delay in Pentagon research for alternative to 'forever chemicals' Senate Democrats demand White House fire controversial head of public lands agency House Democrats tee up vote on climate-focused energy bill next week MORE further complicates the party’s chances of coming out with a net victory.

But the party’s left flank is convinced that a full embrace of progressivism is the only way to return to power, and it is ready to fight for the party’s soul.

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“We fundamentally reject the assumption that Democrats can only win in red states by pandering to racists and big bankers,” said Claire Sandberg, a co-founder of the progressive political action committee We Will Replace You.

“The way we beat Trumpism and take back Congress and statehouses is offering a coherent vision of our own to put people back to work. … We don’t need to completely compromise our own values and principles.”

We Will Replace You is the most visible effort gearing up to back primary challenges from the left. Spearheaded by a group of progressives, including two former senior staffers on Sen. Bernie Sanders Bernie SandersNo new taxes for the ultra rich — fix bad tax policy instead Democrats back away from quick reversal of Trump tax cuts The Memo: 2020 is all about winning Florida MORE’s (I-Vt.) presidential campaign, the group’s website includes a warning for Democrats looking to avoid a competitive primary race.

“Do everything you can to Resist Trump, or we will replace you with someone who will,” the group’s statement reads.

The minimum qualifications for avoiding progressives’ wrath, the website adds, include voting against every Trump administration nominee, fighting against the confirmation of Judge Neil Gorsuch to the Supreme Court, being willing to slow down the legislative process to block the president’s agenda and pushing for the ouster of controversial chief strategist Stephen Bannon.

It’s a high bar, and one that not even Sanders has met. He voted to confirm three of Trump’s Cabinet picks: Homeland Security Secretary John Kelly, Defense Secretary James Mattis and Veterans Affairs Secretary David Shulkin, who received unanimous confirmation.

Considering no senator has hit that bar, the group is likely to use those qualifications as a guide instead of as a red line.

We Will Replace You and similar efforts are the next step for aggrieved progressives convinced that Sanders’s populism could have bested Trump in November’s presidential election.

That frustration only increased after progressives’ preferred candidate to lead the Democratic Party, Minnesota Rep. Keith Ellison, lost the race for chairman of the Democratic National Committee (DNC) last weekend to former Obama administration Labor Secretary Tom Perez.

In a DNC debate last week, Perez said that he supports the party remaining neutral in primaries.

Sanders himself has avoided blessing the effort outright. He’s focused instead on a broad call for a shift toward populism but hasn’t specifically addressed the tactical merits of primaries.

With a staff that includes adviser Kenneth Pennington, who helped to spearhead Sanders’s massive digital fundraising effort, We Will Replace You is hoping to have a grassroots army of donors to power its fight. The group is set up to both donate directly to candidates and, using a different account, make independent expenditures.

While the group waits to see how senators respond in the age of Trump before settling on firm targets, Manchin has already become its top antagonist.

First, Politico released audio of Manchin challenging Sanders supporters to field a primary challenger against him. Shortly after that, Axios reported that he had participated in an off-the-record session with conservative outlet Breitbart News, which Bannon ran before joining the Trump campaign.

That drew a biting statement from We Will Replace You, which called on Manchin to be dumped from Senate leadership.

Manchin has voted for more of Trump’s nominees than any other Democrat, supporting all but four. Manchin’s willingness to go along with Trump reflects voter pressure in his state, which Trump won by more than 40 percentage points over Democratic presidential nominee Hillary Clinton Hillary Diane Rodham ClintonBiden courts veterans amid fallout from Trump military controversies Biden looks to shore up Latino support in Florida MLB owner: It's 'very necessary' to vote for Trump MORE.

Others up for reelection in states Trump carried — including Sens. Heidi Heitkamp Mary (Heidi) Kathryn HeitkampCentrists, progressives rally around Harris pick for VP 70 former senators propose bipartisan caucus for incumbents Susan Collins set to play pivotal role in impeachment drama MORE (N.D.), Claire McCaskill Claire Conner McCaskillDemocratic-linked group runs ads in Kansas GOP Senate primary Trump mocked for low attendance at rally Missouri county issues travel advisory for Lake of the Ozarks after Memorial Day parties MORE (Mo.), and Joe Donnelly Joseph (Joe) Simon DonnellyEx-Sen. Joe Donnelly endorses Biden Lobbying world 70 former senators propose bipartisan caucus for incumbents MORE (Ind.) — voted in favor of the majority of Trump’s Cabinet picks.

But while Sanders won the Democratic primaries in states such as West Virginia and Missouri, it’s unclear whether national progressive outrage will translate into consequences for these lawmakers in their own states.

It’s virtually the same tactic that led to establishment Republicans fighting through the early part of President Obama’s tenure to keep their incumbents free from primary challenges. Though Tea Party activists focused on challenging GOP incumbents in primaries managed to sometimes replace a lawmaker with someone more conservative, they also lost winnable general election races in states like Indiana and Missouri after winning the primaries.

It’s difficult and expensive to unseat a sitting senator within your own party, even with the perfect candidate. In states such as West Virginia, the Democratic bench doesn’t include an obvious choice for a progressive candidate.

And many Democrats warn that a primary challenge could hamper the party’s chances of keeping these vulnerable seats by either suppressing turnout within the party or turning away swing voters.

After the party missed its best chance at winning Senate control, in 2016, next cycle’s map could turn disastrous for the party. A Republican wave could threaten to move Republicans closer to a filibuster-proof 60-vote majority in the Senate, meaning near-total control of the federal government.

That’s the dire situation painted by South Carolina Democratic Party Chairman Jaime Harrison, who warned against primary challenges during last week’s DNC chair debate.

“If Democrats want to be in a permanent minority, let’s spend all of our time and energy fighting each other,” he said.

“But if we want to actually fight back against Donald Trump, let’s spend our energy going after [Sen.] Ted Cruz Rafael (Ted) Edward CruzHealth care in the crosshairs with new Trump Supreme Court list 'Parks and Rec' cast members hosting special reunion to raise money for Wisconsin Democrats Jimmy Carter says his son smoked pot with Willie Nelson on White House roof MORE [R-Texas]. Let’s spend our energy going after the Republicans that are up.”

But liberal activists such as Nomiki Konst, who is also a journalist for The Young Turks online news show, told The Hill that more moderate members of the party are “holding the party hostage” by not allowing it to be more responsive to the progressive left.

Konst echoed Sandberg about the power of electoral consequences: that a progressive strategy will ultimately motivate the base and appeal to some Trump voters, leaving Democrats better off in a general election.

“We think that the greatest danger in 2018, with so many Democratic incumbents having to defend their seats, is that the Democratic base won’t feel inspired to turn out in what’s going to come down to a turnout election,” Sandberg said.

“The plea for Democrats to turn out to polls may fail to motivate many Democratic voters if they don’t see those same Democrats fight the Trump administration.”

And while many Democratic leaders may be concerned about the electoral risks of primary challenges, some believe that the best plan is to let the process play out.

Sally Boynton Brown, a Idaho Democratic Party executive director who ran for DNC chief, told The Hill that the best thing for the party structure to do at all levels is to make sure there’s an open dialogue so everyone is aware of their options.

“In some of these states where we are hearing about folks wanting a primary, if we lost that [lawmaker], the chances of winning that seat back are very slim,” she said.

“I get that it’s scary. But I think you ultimately have to trust the democratic process and trust that the people who are supporting the Democratic senator or representative to step up to the plate and defend their record.”

--This story was updated at 7:53 a.m.