Supporters of presidential candidate Bernie Sanders Bernie SandersMcConnell accuses Democrats of sowing division by 'downplaying progress' on election security The Hill's Campaign Report: Arizona shifts towards Biden | Biden prepares for drive-in town hall | New Biden ad targets Latino voters Why Democrats must confront extreme left wing incitement to violence MORE are lashing out at Sen. Elizabeth Warren Elizabeth WarrenWarren, Schumer introduce plan for next president to cancel ,000 in student debt The Hill's 12:30 Report - Presented by Facebook - Don't expect a government check anytime soon No new taxes for the ultra rich — fix bad tax policy instead MORE (D-Mass.) for staying neutral in the Democratic primary.

Some Sanders fans are particularly upset that Warren didn’t tilt the scales in the Vermont senator’s favor in her home state of Massachusetts, where Hillary Clinton Hillary Diane Rodham ClintonHillicon Valley: FBI chief says Russia is trying to interfere in election to undermine Biden | Treasury Dept. sanctions Iranian government-backed hackers The Hill's Campaign Report: Arizona shifts towards Biden | Biden prepares for drive-in town hall | New Biden ad targets Latino voters FBI chief says Russia is trying to interfere in election to undermine Biden MORE pulled out an important win on Tuesday.

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“Senator Warren, you’re all talk, no walk. Used to respect you but now I’ll take that respect and give it to Tulsi Gabbard Tulsi GabbardRepublicans call on DOJ to investigate Netflix over 'Cuties' film Hispanic Caucus campaign arm endorses slate of non-Hispanic candidates Gabbard says she 'was not invited to participate in any way' in Democratic convention MORE, who actually deserves it,” said one commenter on Warren’s Facebook page, referring to the Hawaii lawmaker who recently stepped down from a position at the Democratic National Committee to back Sanders.

A glance at Warren’s social media shows that she is inundated by Sanders backers, who are offering a combination of pleas and recriminations over her choice not to endorse so far.

One recent post on her Facebook page about paid family leave had more than 1,000 comments, and nearly all were about her not endorsing Sanders.

“Coward,” said one critic with a Sanders logo for an avatar.

The online fervor over a potential Warren endorsement is so high that The New York Times had to publicly disavow a fake news article announcing Warren was backing Sanders.

Warren, who did not comment for this story, has been feeling pressure from all sides in the fractious Democratic battle.

She’s the only woman in the Senate who hasn’t endorsed Clinton, and her colleagues have pressed her to do so.

“I’m hopeful she’ll join us. I’m hopeful she’ll join the revolution that will allow us to come together to elect” the first female president, Sen. Debbie Stabenow Deborah (Debbie) Ann StabenowGAO report finds brokers offered false info on coverage for pre-existing conditions Democrats back away from quick reversal of Trump tax cuts Battle looms over Biden health care plan if Democrats win big MORE (D-Mich.) told The Hill last month.

There’s no real doubt that Warren will eventually endorse the Democratic nominee for the White House.

Warren’s outsize presence in the Democratic Party virtually ensures her a plum speaking spot at the national convention, where she could play a role in uniting the party.

Leaders of liberal groups backing Sanders for president say they’re not bothered by her neutrality and credit her with helping to move Clinton to the left.

“I don’t think she’s been on the sidelines,” said Charles Chamberlain, executive director of Democracy for America, which has endorsed Sanders. “What she does is hugely helpful for Bernie. She continues to keep the campaign focused on the issues.”

Chamberlain also said Warren’s decision not to endorse Clinton yet is actually an implicit endorsement of Sanders.

“She’s the only female senator who has not made an endorsement of Hillary Clinton. That’s almost an endorsement right there,” he said. “It is saying, flat out, that I won’t just go along to get along.”

The anger Warren sees from the most vociferous Sanders supporters does not mean she’s in bad graces with most people on the left, either.

Videos she posts to her Facebook page pull in millions of views, underlining the fact that she remains one of her party’s most popular figures and a progressive hero.

Given that standing, many believe Warren could be a central player in rallying the party around its nominee after a tough primary.

“There’s a growing belief that Elizabeth Warren will play a large role during the unification moment,” said Adam Green, co-founder of the Progressive Change Campaign Committee, which has not endorsed in the primary. “Her influence is right in the middle of the race, and it’s because her hands are clean and she hasn’t endorsed one candidate.”

Warren could also be maximizing her leverage by not endorsing a candidate.

“If you endorse Bernie now, then you’ve marginalized yourself,” said one financial lobbyist who has watched Warren closely for years. “Why would you do it now, when you already have somebody who’s bringing Hillary over to the left?

“I don’t want to overstate it, but she is the most important person in the party in many ways,” the lobbyist added. “She is the person that everybody needs.”

Throughout the primary, Warren has offered praise for both Clinton and Sanders, often when they have taken a tougher stance on overseeing Wall Street.

She praised Sanders’s financial reform plan, which includes breaking up the nation’s biggest banks, and also offered kudos to Clinton for vowing to fight against GOP efforts to roll back the Dodd-Frank financial reform law.

“She’s been very good about rewarding them,” said Green. “Once someone has endorsed, there’s not much reason for the other candidate to listen to them.”

One area where Warren would like to exert some influence is on the staffing of the next Democratic administration.

She has picked fights with the Obama administration over high-ranking officials she deems unsatisfactory. She has repeatedly challenged watchdogs like the Securities and Exchange Commission and the Justice Department for what she sees as a lax approach to financial wrongdoers. And she upended the White House’s efforts to place Antonio Weiss, a former investment banker, in a top Treasury Department position. Weiss ultimately ended up in an advisory role at Treasury.

And Warren made clear in a January op-ed in the Times that she will be expecting the eventual Democratic nominee to promise tough-minded regulators.

“Personnel is policy,” she wrote. “The next president can rebuild faith in our institutions by honoring the simple notion that nobody is above the law, but it will happen only if voters demand it.”