Sens. Bernie Sanders and Elizabeth Warren, rivals for the affections of the Democratic Party’s left wing, are increasingly making careful but unmistakable efforts to distinguish themselves from each other as the primary heads toward its first vote in three months.

In an interview with ABC News published Sunday, Sanders criticized Warren’s recently released plan for funding Medicare-for-all, which aimed to separate Warren from Sanders by avoiding the middle-class tax hikes that he says the plan would require.

Their maneuvering is also extending beyond health care, as Sanders campaigned Sunday night before a crowd of more than 10,000 with one of his prize endorsers, Rep. Ilhan Omar (D-Minn.). Sanders plans to travel to Iowa next weekend with another high-profile backer, Rep. Alexandria Ocasio-Cortez (D-N.Y.).

The endorsements of those congresswomen helped show off Sanders’s appeal to some of the party’s most visible young liberals and minorities. Warren — who is also seeking to appeal to a new, diverse generation of liberals — was introduced by another liberal congresswoman, Katie Porter (D-Calif.), on Sunday in Davenport, Iowa.

However, it was the battle over Medicare-for-all that took center stage in the past 24 hours. Sanders said his approach to funding Medicare-for-all, which includes raising taxes on middle-class families, is “far more progressive” than Warren’s method, a stinging comment calculated to solidify his role as the only pure progressive in the race.

Sanders took issue specifically with Warren’s proposal that businesses would redirect their current health-care payments to the Medicare program, which Sanders said would hurt job growth.

“I think that that would probably have a very negative impact on creating those jobs or providing wages, increased wages and benefits for those workers,” Sanders told ABC. “So I think we have a better way, which is a 7.5 percent payroll tax, which is far more I think progressive. Because it will not impact employers of low-wage workers, but hit significantly employers of upper-income people.”

Asked about Sanders’s criticism at a campaign event Sunday, Warren sought to reaffirm their shared outlook.

“Bernie may have a different vision of how to pay for it, but let’s be really clear: Bernie and I are headed in exactly the same direction,” Warren said. “And that is the $11 trillion that families are going to pay over the next 10 years in out-of-pocket medical costs will go away.”

But she disputed Sanders’s contention that her plan would hurt employers, saying they would pay slightly less than they do now and would save on human resources costs associated with wrangling with insurance companies.

“So this is something that’s going to help employers,” Warren said.

Sanders’s campaign is seeking to find a balance, voicing differences with Warren while refraining from overly sharp attacks. Unlike Sanders’s disagreements with former vice president Joe Biden, which his aides are eager to amplify, they are treading more carefully around Warren.

Nina Turner, a co-chair of the Sanders campaign, said Sunday that while she thinks Sanders should draw more contrasts with Warren, his operation cannot focus on her alone.

“I know it’s this push to make it just about those two, but last time I checked, there are a lot of candidates still in this race,” Turner said. She added, “I’m not trying to be cute with this, but the entire Democratic platform is based on what Senator Bernie Sanders put out there in 2016. Everybody is trying to figure out where they fit in that.”

Still, the growing divergence of the two progressives played out during a weekend widely seen as a kickoff of sorts, the start of crunchtime for candidates hoping for a strong showing in Iowa’s first-in-the-nation caucuses on Feb. 3. As a result, criticisms flew from one candidate to the other all weekend as the contenders traipsed to various campaign events around the state.

Sanders had largely avoided the back-and-forth, which included Warren’s suggestion Friday night that moderates did not have the courage to make big change. South Bend, Ind., Mayor Pete Buttigieg suggested Saturday that the primary had become a two-person race between him and Warren. Biden argued that policy disagreements are not grounds for the kind of character attacks he says Warren and others are making.

As he began an open-press bus tour across Iowa, Buttigieg backtracked somewhat from his comment about the race being between him and Warren, but he continued to train much of his fire on the senator from Massachusetts. “I think Medicare-for-all is unpopular because it’s not the best policy,” said Buttigieg, who favors an optional version of the plan that he calls “Medicare for all who want it.”

Sanders and Warren had been locked in a fragile detente for months. They have been largely unwilling to attack each other, partly to avoid alienating voters should one of them drop out and need to court the other’s backers.

But as the Iowa caucuses approach and the field begins to shake out, Sanders has increasingly drawn careful lines between the two, a pattern that intensified this weekend with the Medicare-for-all fight and the Omar rally.

Pressed in recent interviews on the differences between himself and Warren, Sanders has not shied away from the question as he did earlier in the campaign.

“Elizabeth, I think, as you know, has said that she is a capitalist through her bones. I’m not,” Sanders said in an early October interview on ABC’s “This Week.”

Asked in a subsequent interview with PBS how his worldview is different from hers, the senator from Vermont said he and Warren have worked together a lot in the Senate, before adding, “I think that the only way we bring about real change in this country is not within Capitol Hill. What I believe is we need a political revolution.”

Speaking to CNBC’s John Harwood about the differences between himself and Warren, Sanders said, “It’s not just more regulation. It’s about involving millions of people — working people, young people, people who believe in justice — in the political process, to tell the corporate elite that enough is enough.” Warren has made regulating Wall Street and tightening restrictions on large corporations a core part of her pitch.

Warren has been more circumspect about directly taking on Sanders. But her detailed policy plans often seem aimed at demonstrating that while she is as revolutionary as Sanders, she is more realistic and electable. Warren’s release of her Medicare-for-all funding plan — along with her pointed statement that it avoids taxing the middle class — brings the skirmish into the open.

Sanders has estimated Medicare-for-all, his signature policy proposal, will cost $30 trillion to $40 trillion over 10 years. His campaign has clarified that because he would use the spending already going toward Medicare, Medicaid and other health-related government programs, he would need to come up with only about $15 trillion in new revenue.

Unlike Warren, Sanders has said he would pay for it in part with higher middle-class taxes. He has mentioned a 4 percent tax on income over $29,000, but he argues those increases would be offset by health-care savings because families would no longer pay premiums, co-pays or other out-of-pocket expenses. Sanders is also proposing to raise taxes on the wealthiest Americans to help pay for his plan.

Still, his campaign has not been able to say at which income level Americans will start paying more in taxes than they are saving in health-care costs, and it’s not a question Sanders has shown any urgency to answer. In the CNBC interview, Sanders said he didn’t feel the need to present specific blueprints for how different taxpayers would be affected by his plan.

“The fight right now is to get the American people to understand that we’re spending twice as much per capita [than other countries], that of course we can pay for it,” Sanders said. “You’re asking me to come up with an exact detailed plan of how every American — how much you’re going to pay more in taxes, how much I’m going to pay. I don’t think I have to do that right now.”

Warren, who has begun taking the lead in some primary polls, was navigating fire from all angles over the weekend. She was criticized for seeming to tell reporters in Dubuque, Iowa, that her new health-care funding plan would not raise taxes on anyone but billionaires.

“For Medicare-for-all, it’s a billion dollars,” she said when pressed on the cutoff, adding, “This is no increase in taxes for anyone except billionaires. Period. Done.”

But the plan involves raising capital gains taxes for the wealthiest 1 percent of Americans, one of several aspects of her plan that would affect some people with wealth less than $1 billion.

Biden’s campaign seized on the comments, calling into question Warren’s honesty about the issue.

“Senator Warren said tonight that her single-payer plan won’t raise taxes on anyone but billionaires, but that’s simply not true,” Kate Bedingfield, Biden’s deputy campaign manager, said in a statement.

A spokeswoman for Warren’s campaign said she had been referring only to the “wealth tax” component of her plan. Under her Medicare-for-all funding proposal, a wealth tax on people with a net worth of more than $1 billion would rise from 3 percent to 6 percent. (The tax on those with assets between $50 million and $1 billion would remain at 2 percent.)

Complicating the interplay between the two senators, despite their similar left-wing credentials, many supporters of Sanders and Warren do not necessarily identify the other as their second choice. Some working-class voters appear to see appeal in Biden as well as Sanders, for example, while some educated, urban Democrats are attracted to Buttigieg as well as Warren.

Lindsay James, an Iowa state representative who has endorsed Warren, said voters in blue-collar communities in eastern Iowa do have questions about how to pay for a single-payer system like Medicare-for-all. But those questions pale next to their concerns about the inadequacies of the current system, she said.

“The people that I’m talking to who are securely at this moment in the middle class have questions and concerns. But for my constituents — for the woman who spent 10 years digging her way out of medical bills after her daughter beat cancer — financial security is being able to buy pizza,” James said. “The bulk of our country is reeling under the health-care realities that we face.”

James said she chose to support Warren after considering a number of other contenders — praising Sens. Kamala D. Harris of California and Cory Booker of New Jersey, as well as But­tigieg.

That cluster of candidates reaffirms that a loss for Warren or Sanders is not necessarily a gain for the other. In Sanders’s case, some of his supporters suggest they would vote for a third-party or lesser-known candidate if he drops out.

For now, the most urgent question facing Warren is whether her release of a complex funding plan that includes new taxes and corporate requirements will turn off voters who may be open to more centrist candidates or who worry that such far-reaching proposals will make it harder to defeat President Trump.

Sue Telsrow, a 66-year-old retiree who attended Warren’s town hall on Saturday in Dubuque, said she was also considering Harris and Buttigieg. Telsrow, who is on Medicare, said the sweeping health-care overhaul backed by Warren worried her “a little,” but she was “open to it.” Her concern was that the plan was simply “too unwieldy, possibly tying up too many government resources.”

So while Sanders and Warren share the need to overcome concerns about Medicare-for-all, they are also trying to demonstrate with growing urgency that they don’t share everything.