Joe Biden is sharing the presidential primary’s top tier with two progressive senators. One, he says, levied an unprompted attack against his commitment to the Democratic Party and exhibits “elitist” behavior. The other, he stresses with striking frequency, is “honest” and, in the most Senate-speak way, a friend.

“Bernie’s been honest; he’s going to raise taxes on middle class,” Biden said in July at a convention in Detroit about Sen. Bernie Sanders’ (I-VT) approach to funding Medicare for All, a progressive policy that Biden’s campaign says is not the best way to cover Americans’ health care needs.

Since then, the former vice president become more consistent with his praise. “First and foremost, the thing you must do in public life is be honest with the public,” he said on Monday night during a CNN town hall addressing the same topic. “Bernie's been honest.”

The same amount of honesty on the subject, he suggested, does not apply to Sen. Elizabeth Warren (D-MA), who waited longer than her primary rivals to release details of her Medicare for All proposal, including the funding behind it. “Let's get something straight. She attacked me!” Biden said during the town hall about Warren, who suggested he is running in the wrong party’s primary and accused him of repeating Republican talking points. “It’s not about her,” he added when asked by the moderator about calling her “elitist.” “It’s about the attitude that exists right now. If you disagree with me, you must be bad.”

That dynamic — Biden responding to or ramping up criticism of Warren, while oftentimes going out of his way to praise Sanders’ honesty — has been escalating in recent weeks. With less than three months until the Iowa caucuses, the former vice president has sharpened his messaging against the Massachusetts senator over substance and style, and has largely left Sanders, who also remains a top-tier contender for the Democratic nomination, alone.

While the two politicians in their late seventies voted in opposite directions on a variety of high-stakes decisions (including to authorize the Iraq War and NAFTA, which Biden was for and Sanders was against), they have enjoyed a generally collegial Senate relationship. Sanders often refers to Biden as his “good friend” whom he disagrees with on many issues. And Biden tends to do the same.

“I know genuinely the senator does have a respect for Vice President Biden,” a senior Sanders 2020 campaign adviser told The Daily Beast. “They’ll joust on the debate stage, that’s as far as it will go.”

In contrast, his relationship with Warren, dating back at least 17 years, is illustrated in vivid detail during a 2005 Senate Judiciary Committee hearing over a bankruptcy bill that Biden supported and Warren was adamantly against. There were several terse exchanges leaving little doubt what the two thought of each other. But even before that hearing, Warren was not a fan. In her 2003 book, The Two-Income Trap: Why Middle-Class Parents Are Going Broke, Warren wrote that Biden’s support of the bill that she believed hurt low-income women in particular was hypocritical. “Senators like Joe Biden should not be allowed to sell out women in the morning and be heralded as their friend in the evening,” she wrote. In 2013, when Warren was being sworn into the Senate, Biden quipped: “You gave me hell.”

“The personal animus is a big part of it,” Karthik Ganapathy, who served as the battleground states communications director for Sanders’ 2016 campaign but is currently unattached, said about the dynamic between Biden and Warren that has largely excluded Sanders.

Biden’s advisers say giving brownie points to Sanders for honesty is nothing more than simply conveying the timeline and fact pattern that has unfolded in the months-long health-care discussion, when he was up front with voters about raising taxes from the get-go.

“I think that [Biden] has acknowledged that Sanders has been upfront about it because he has,” a Biden campaign adviser said about the thinking behind the praise. “And [Warren] hasn’t.”

To be sure, Biden’s campaign has not always left Sanders alone. Campaign officials and surrogates have frequently hit back against the Vermont Independent on Twitter and in several news stories, largely over health care, which remains a top priority for Democrats. In an October interview with CNBC, Biden’s deputy campaign manager Kate Bedingfield questioned Sanders’ “credibility” for declining to say how he would pay for Medicare for All.

“It’s alarming that Senator Sanders, who has been up-front for years that Medicare for All would require middle-class tax hikes, won’t tell voters ‘right now’ how much more they will pay in taxes because of his plan,” Bedingfield said. “When you’re running to take on the most dishonest president in American history,” she added, “Senator Sanders and others who back Medicare for All have to preserve their credibility.”

But over the past two weeks, as Biden has sharpened his response to Warren, Sanders has appeared to be less of a priority, multiple strategists, pollsters, current and former campaign advisers noted.

Biden’s “more worried about her candidacy than he is about Sanders’,” Andy Smith, a University of New Hampshire pollster, said about Warren. “They don’t think Sanders is as much of a threat.”

While Biden has fallen in some surveys in New Hampshire, the first primary state that follows just eight days after the Iowa caucus, polling averages indicate it’s a neck-and-neck race. In the latest Real Clear Politics polling average in the Granite State, Biden and Warren are dead even at 19.7 percent, with Sanders at 19 percent, representing a statistical tie.

In Iowa, the top tier is also volatile. The latest Monmouth University poll shows South Bend Mayor Pete Buttigieg narrowly topping the crowded Democratic field there, earning 22 percent of support, compared to Biden’s 19 percent, just one point away from Warren’s 18 percent. Sanders comes in a distant fourth place at 13 percent.

“If [Biden] drives people away from Sanders, he’s driving them into Warren’s camp,” Patrick Murray, director of the Monmouth University Polling Institute, told The Daily Beast.

In another scenario: “A stronger Bernie means a weaker Warren,” Sean McElwee, co-founder of Data for Progress, a nonprofit progressive think tank, said. The senior Sanders adviser echoed that point, adding that Biden and Sanders both pull from a similar coalition of working class voters.

“From a political standpoint, it does not benefit Vice President Biden,” the senior Sanders’ adviser said about attacking the Vermont senator.

Multiple strategists and campaign officials said that if Warren is a more immediate threat to Biden, praising Sanders as “honest” can be a way to indirectly dig her, without having to go negative on his former Senate colleague who shares many of her progressive policies.

“I don’t think it’s necessarily about Bernie,” Joe Trippi, a longtime Democratic campaign operative, said. “It’s a way of saying ‘Bernie’s not being political about this. He’s telling you the truth about his policy and I’m telling the truth about mine.’”

Warren took heat for stalling on the health-care details, which Trippi said was part of her problem. “It’s not that she’s for Medicare for All, it’s that she’s being political,” he said.

Other Democrats say that if Biden attacks Sanders in a similar way to Warren, it would probably be in vain. Sanders still enjoys a loyal liberal following, part of which carried over from 2016. In the latest Quinnipiac Poll in New Hampshire, 57 percent of Sanders’ voters said they had made up their mind to support him, while the corresponding number for Warren was 29 percent.

“If you go after him, A, you’re not going to convince [Sanders’ supporters] and B, you risk alienating a big chunk of the base,” Ganapathy said about Biden. “If it’s not going to win you votes, why would you do it?”