As Sunday turned to Monday, Briahna Gray, national press secretary for Sen. Bernie Sanders’ presidential campaign, posted a series of criticisms of Sen. Elizabeth Warren (D-Mass.) on Twitter. Gray began with subtlety, highlighting a speech the Vermont senator gave on the House floor in the 1990s in support of gay military veterans and service members. And, in what appeared to be a subtweet at Warren, she noted that Sanders delivered the speech at a time when “your fave was still ‘evolving’ (read ‘triangulating’) on gay rights.” (In a follow-up conversation, Gray would not say to whom she was referring when she said “fave.” Warren supported same-sex marriage during her first Senate run in 2012, prior to former President Barack Obama’s “evolution.”) Next, Gray noted that under Sanders’ pro-union legislation, Warren’s campaign would be forced into mediation for failing to reach a collective bargaining agreement so many months after recognizing its campaign staff’s union. Finally, in a post shortly after midnight, Gray slammed Warren’s refusal to endorse a national rent control law, echoing a critique voiced earlier in the weekend by left-wing activists. She suggested that it contradicted Warren’s self-described can-do attitude toward other ambitious policies. Gray’s comments in themselves were not out of the ordinary. Sanders campaign aides are notoriously feisty and independent on social media ― a marked contrast with the boringly disciplined etiquette of other campaigns’ staffers. But when HuffPost reached out on Monday to clarify whether Gray’s remarks were part of a shift toward more explicit confrontation with Warren, the campaign directed HuffPost to Gray, who stood by her remarks.

Primary campaigns are about drawing contrasts between candidates so that voters can make an informed choice between them. Briahna Gray, Sanders campaign

“Primary campaigns are about drawing contrasts between candidates so that voters can make an informed choice between them,” Gray said in a statement. Sanders and Warren reportedly struck a non-aggression pact in December prior to launching their respective campaigns. The much-vaunted détente survived two nationally televised debates in which the two contenders shared a stage. They eschewed the moderators’ efforts to drive a wedge between them in favor of teaming up against moderate rivals. Even in the course of a conversation about this article, the Sanders campaign wanted to emphasize his high regard for Warren. “Sen. Sanders respects Sen. Warren and values his friendship with her,” Mike Casca, a senior communications adviser for the Sanders campaign, said in a statement. “They’ve been longtime allies in fighting to improve the lives of working Americans.” But though Sanders himself has yet to criticize Warren, his aides and surrogates have been taking gradually bolder shots at the Massachusetts senator. The non-aggression pact is fraying. Gray’s remarks follow more implicit steps in this direction by other Sanders lieutenants. Amid left-wing uproar over the Working Families Party’s endorsement of Warren, top Sanders spokesman Mike Casca gave his blessing to calls for the WFP to release a breakdown of its endorsement vote that would show whether the group’s national delegates overrode the will of pro-Sanders dues-paying members and activists. The following day, when Sanders received his millionth donor, Sanders campaign manager Faiz Shakir noted that Sanders is the only candidate to rule out high-dollar private fundraisers for the primary as well as the general election. The observation was a veiled ding at Warren, who has said that in the interest of defeating President Donald Trump, she would resume courting wealthy donors during the general election. Just a few weeks ago, HuffPost reported that the Sanders campaign saw supporters of former Vice President Joe Biden as riper targets for persuasion. The campaign had a custom-made text message response for Biden backers, but only a generic one for voters leaning toward other candidates. But Warren’s rise, reflected in everything from the WFP endorsement to new polling showing her winning more of Sanders’ 2016 voters than Sanders himself, has raised the specter of her supplanting Sanders as the go-to progressive alternative to Biden. The campaign aides’ jabs at Warren, however tame and haphazard, provide an official imprimatur to a broader argument that Sanders surrogates and partisans have been making more openly for some time: that Warren’s progressive bona fides are questionable and that she is a flawed general election candidate. Below is a summary and explanation of their various claims against her. The Warren campaign declined to comment for this story.

Lucas Jackson / Reuters Bernie Sanders, left, greets Elizabeth Warren at the July 30 debate in Detroit, Michigan. The two candidates reportedly had a non-aggression pact that is now unraveling.

Warren Opposes A National Rent Control Law The most recent pile-on against Warren kicked into gear over the weekend when she addressed the Iowa Center for Community Improvement Action Fund’s candidate forum in Des Moines, Iowa. An activist pressed Warren on whether she would back national rent control legislation, which would cap annual rent increases across the country. Warren said that she would fight to ensure that localities are free from state laws that prevent them from pursuing rent control on their own, but would not back a national rent control law. “Writing a rent control plan in Washington may work for Chicago, but it’s not gonna work for Iowa City or it may not work for Dallas,” she said. Warren introduced an affordable housing bill in March that would allot $10 billion in grants that cities and regions could compete for, provided that they end restrictive land-use policies. It would also give cities that enact tenant protections like rent control opportunities for additional cash. “My administration will also take whatever legal steps it can to stop states from preempting local efforts to enact tenant protection laws,” she wrote in a Medium post outlining her housing plans. Warren would also invest $500 billion in building or restoring affordable housing ― a figure she pays for by restoring the estate tax to its 2009 level. And she wants to create a home-buying assistance program for first-time buyers in historically redlined neighborhoods to narrow the Black-white wealth gap.

Writing a rent control plan in Washington may work for Chicago, but it’s not gonna work for Iowa City or it may not work for Dallas. Sen. Elizabeth Warren (D-Mass.)

Sanders, by contrast, would cap all annual rent increases at the higher of either 3% or 1.5 times the rate of inflation. Cities would be able to go further and landlords could apply for exemptions from the rule if they make major capital investments in a property. For some left-wing activists, particularly those living in expensive cities, making rent control “universal” ― or at least expanding it ― has become a priority nearly as urgent as achieving single-payer health care. Rep. Alexandria Ocasio-Cortez of New York, who volunteered for Sanders in 2016, introduced a rent control bill on Wednesday that also caps rent hikes at 3%. As a result, a video of Warren’s exchange with the activist in Iowa posted by California-based labor organizer Brett Banditelli sparked biting criticism of Warren on social media. For example, Cea Weaver, who helped pass New York state’s new rent regulations, suggested that Warren’s lack of interest in national rent control reflected an elitist reliance on economic orthodoxy. Gray, the Sanders campaign aide, embedded Banditelli’s video in her critical tweet as well. “Bernie says yes to [national] rent control [because] we can, we should, & we must,” she wrote. Analilia Mejia, the Sanders campaign’s political director, also highlighted the contrast between the two candidates’ platforms on Twitter. “There just isn’t a comparison,” she wrote.

Alex Wong/Getty Images Sanders, seen here at a budget conference in Nov. 2013, introduced a single-payer health care bill that year that received no support from colleagues. Supporters value his consistency.

Warren Can’t Be Trusted To Fight For ‘Medicare For All’ Beginning with the first Democratic presidential debate in June, Warren has repeatedly affirmed her support for Sanders’ single-payer “Medicare for All” health care legislation. When pressed about the bill’s prohibition on all but very limited forms of private health insurance ― a provision that has stirred the most political jitters ― Warren has endorsed it time and again. Two presidential rivals, Sens. Kamala Harris of California and Cory Booker of New Jersey, have, by comparison, backed away from Sanders’ bill despite co-sponsoring it in the Senate. But some Sanders partisans note that Warren, a recent convert to the Medicare for All cause, still has not made it a major feature of her stump speech. She barely mentions the policy unless she is asked about it, and she has refused to explicitly say she would back middle-class taxes to pay for it. That has raised fears that Warren would not fight for it once in office, which Medicare for All proponents consider a prerequisite for its eventual passage. “She’s simultaneously trying to tap into the activist energy and enthusiasm that activists have spent years building for single-payer and Medicare for All … without forfeiting any of the plausible deniability or the support of people who wouldn’t want to go that far,” Natalie Shure, a member of the Boston chapter of the Democratic Socialists of America, told HuffPost. During a campaign event Wednesday in New Hampshire, Warren sparked a new round of skepticism when she described Sanders’ “Medicare for All” legislation, which she has co-sponsored, as a “framework.” “What we’ve got in Medicare for All is a framework, and it doesn’t have the details, and you’re right to be asking, but the most important part of your asking is to raise awareness so we get this right as we go through it,” Warren said. The remark prompted a swipe from Sanders’ senior adviser Warren Gunnels, who disputed Warren’s word choice on Twitter. Medicare for All “isn’t a framework. It’s a 100-page bill,” he wrote.

Lucas Jackson / Reuters Warren speaks to thousands of rallygoers in Manhattan on Sept. 16. Her ascent in the polls appears to have prompted more aggressive pushback from Sanders' team.

Warren Is A Former Republican Who’s Taken Corporate Money Bernie World skepticism of Warren’s support for Medicare for All is rooted in a broader suspicion of her more recent arrival at stances Sanders has held for decades. They argue that she is less trustworthy in general because she has admitted to being a registered Republican until the mid-1990s. (Her research into the struggles of families declaring bankruptcy prompted her to leave the GOP, according to Warren.) Susan Sarandon, an Oscar-winning actor and prominent Sanders campaign surrogate, caused a stir in August when she took a veiled swipe at Warren while introducing Sanders at a campaign event in Iowa. Sanders, she said, “is not someone who used to be a Republican. He is not someone who used to take money — or still takes money — from Wall Street. He is the real deal.” Sarandon’s remarks about taking money from Wall Street might refer to Warren’s courtship of wealthy donors, including some from the financial world, during her 2018 Senate reelection campaign. She transferred over $10 million left over from that campaign to her presidential run before announcing that she would shun the fundraisers during the Democratic primary. (Warren’s campaign has noted that big-ticket fundraisers accounted for only one-quarter of her total haul in 2017 and 2018.) John Cusack, another actor backing Sanders, introduced him at a rally on Tuesday in Chicago with members of several of the city’s public-sector labor unions. He has echoed Sarandon’s attacks on Warren’s Republican past. “No ones [sic] been more consistent then [sic] Bernie for justice,” he tweeted on Monday night. “Warren was a republican as an adult - glad she figured out supply side economics was a hustle - but come on.”

Ron Sachs-/Pool/Getty Images President Donald Trump gives the floor to a coal miner at the signing of a bill deregulating the industry. Warren's critics doubt her appeal with working-class voters.

Warren Is Less Electable Against Donald Trump In addition to their policy and ideology-based arguments that Warren is not radical enough, prominent Sanders supporters are also claiming that she is less competitive against Trump in a general election. The argument is twofold: First, they point to Warren’s style on the stump and lower rates of support among Democrats without a college degree as evidence that she would have difficulty in a general election. Sanders had a narrow edge among voters with less than a college degree in an August poll conducted by the Pew Research Center, while Warren had a commanding lead over him among voters with advanced degrees. (Biden held the lead for voters at every education level except those with advanced degrees.) Krystal Ball, a co-host of Hill TV’s digital show “Rising,” made the case on Monday that Warren’s appeal is stronger among more educated and successful Democrats because her focus on “plans” appeals to their meritocratic faith in common-sense problem-solving. Warren’s failure to resonate with working-class voters despondent in the country’s institutions make Ball “terrified” that Warren will lose to Trump, the pro-Sanders commentator said. “‘I’ve got a plan for that’ is like a magical elixir to” highly educated Democrats, Ball said. “It says, ‘The experts have been consulted, the white paper has been drafted. We the ascenders of the meritocracy will decide what is to be done about these poor, struggling denizens of the working class.’”

Back in Feb of 2014, I sounded the alarm about HRC and predicted she would lose. Today I'm doing the same with Elizabeth Warren. I like her. I respect her. But I am terrified she will lose to Trump. Here's why. #rising FULL: https://t.co/Lc2eOV3Knlpic.twitter.com/DipRUHQ8FH — Krystal Ball (@krystalball) September 23, 2019

I’m not saying that @ewarren doesn’t have some really bold and gutsy policy positions that I agree with. I love that she’s for a ban on fracking for example- I would definitely vote for her over Trump and her over Biden. And I’d campaign for her if she won the nomination- but... — Josh Fox (@joshfoxfilm) September 8, 2019