Progressive groups backing Rep. Nancy Pelosi’s (D-CA) bid to reclaim the House speaker’s gavel in the next Congress issued a sharp warning on Monday to the group of Democratic lawmakers seeking to deny her the requisite votes: do so at your own political peril.

“If right-wing Democrats end up helping Republicans by voting against Nancy Pelosi as speaker, they can expect to face serious backlash from the same energized and mobilized base of progressive voters that just brought Democrats a majority in the House. Which certainly could extend to primaries,” Karthik Ganapathy, a spokesman for the progressive bulwark MoveOn, told The Daily Beast.

The warning was the latest in an increasingly aggressive exchange of salvos between Pelosi’s detractors and a larger group of supporters. It came just hours after 16 Democrats went public in their vow to oppose her candidacy to lead their caucus—a total that could seriously complicate Pelosi’s ability to corral the 218 votes she needs on the House floor come January.

The question between now and then is whether Pelosi can convince those 11 incumbent Democrats and five incoming freshmen lawmakers who signed onto the letter to reverse their position. An implicit threat from liberal groups—that those lawmakers may face a primary challenger in 2020 if they don’t—could potentially help.

On Monday, Daily Kos—the massive online progressive community that raised more than $8.7 million for Democratic candidates throughout the 2018 midterm cycle—threw its weight behind Pelosi. The group plans to remain heavily involved in the 2020 election cycle, too, and officials left the door open to backing Democrats who challenge Pelosi’s detractors in the primaries.

“We’ll be taking a variety of factors into consideration, including this, and if good challengers run in those seats, we’ll be keeping a close eye on the situation,” communications director Carolyn Fiddler told The Daily Beast.

There are few more dynamic figures in politics than Pelosi, who has led her caucus since 2003 and became the first female speaker in history in 2007. For Democrats, her tenure has been filled with notable policy achievements and difficult election defeats. She is widely regarded as a powerhouse fundraiser and talented vote-getter. But she is also a lightning rod for conservatives and has long been a punching bag for Republican candidates. Those factors have made her a target for removal before ; two years ago, Rep. Tim Ryan (D-OH) won 63 votes to Pelosi’s 134 in the election to be Democratic minority leader.

For progressives, however, the fact that Pelosi was the bogeyman of a midterm cycle in which Democrats still gained the majority lends credence to the idea that she has earned another run at the speakership. So too does the fact that no challenger has yet to emerge against her. Rep. Marcia Fudge (D-OH), who did not sign the insurgent letter, has said she is considering running for the position. The most vocal Pelosi opponents, however, are both white male incumbents who are ideologically more conservative: Ryan and Rep. Seth Moulton (D-MA).

Activists dubbed the initial group of Pelosi opponents as the #FiveWhiteGuys last week. And on Monday night, Moulton encountered swift backlash for his position on Pelosi when he met with constituents at a town hall in his district. Isa Leshko, a 47-year-old Salem resident, organized a protest at the event, distributing stickers indicating that she and other constituents were backing Pelosi.

Leshko, who had previously voted for Moulton and was grateful that he held a number of town halls in the early months of the Trump administration, said that she now believes he is squandering the goodwill he had built up with residents of the district.

“We have worked so incredibly hard to get the House back,” Leshko told The Daily Beast. “And it just feels like he would be squandering the gains that we have made. This really is a slap in the face to progressives and women of color who really are the backbone of the Democratic party.”

“I just can’t see another experienced accomplished talented woman get taken down,” added Leshko, an ardent Hillary Clinton supporter.

A spokesman for Moulton indicated that the Massachusetts Democrat would not be deterred by statements from progressive outfits encouraging primary challengers in the future.

“Seth has made his position on the need for new leadership very clear for over a year and his constituents voted overwhelming to send him back to Congress for another term knowing what that position was,” Moulton spokesman Matt Corridoni told The Daily Beast. “Challenging the status quo and taking on the establishment is always met with resistance from those in power, but the American people—and Seth as one of their representatives—know it’s the right thing to do.”

But Leshko’s sentiments are shared by a host of progressive organizations that have announced their backing of Pelosi during the past week. MoveOn voiced its support around the same time that the leaders of the Congressional Progressive Caucus said they had an encouraging meeting with Pelosi and extracted some key concessions, including the promise of favorable representation on powerful House committees. Indivisible, the “resistance” organization founded when Donald Trump came into office, quickly followed suit, adding that “ we shouldn’t let a small group of white, moderate men sabotage her. We support Nancy Pelosi for speaker of the House.” Some of the Democratic caucus’ most progressive members, including Ilhan Omar of Minnesota, have announced their support for Pelosi, too.

The 11 incumbents who signed Monday’s letter are in relatively safe Democratic districts, which could prompt liberal groups to find and encourage future primary challengers. But the efforts to recruit a viable challenger to Pelosi are also being pushed by a group of newly elected Democrats who campaigned on their opposition to Pelosi.

Absent a decision by the incumbent members to drop their opposition to Pelosi, those members could be forced to take a politically treacherous vote: either torpedoing the party’s primary—if not only—option for speaker, or breaking a campaign promise to help Pelosi win 218 votes.