After a long, steady rise in the polls, Massachusetts Senator Elizabeth Warren is now vying for frontrunner status with former Vice President Joe Biden. Tuesday night, more moderate candidates took aim at her progressive policy positions as unrealistic and expensive.

Medicare for All — the single-payer healthcare plan supported by both Warren and Vermont Sen. Bernie Sanders — was the main topic in this moderate-progressive fight.

Warren has been asked repeatedly about raising taxes on middle-class Americans to pay for that plan. She and Sanders were the two candidates on stage who full-throatedly support the Sanders version of Medicare for All plan. (Booker and Harris were cosponsors, but Harris has now come out with her own plan, and Booker has backed off of his support .)

Moderators asked Warren whether she would raise taxes to pay for Medicare for All and her other plans, "yes or no." Warren instead made points that she regularly makes on this question: her contention that total costs under the plan will go down for middle-class Americans, while the wealthy would foot a large portion of the bill.

"Cost will go up for the wealthy, they will go up for big corporations, and for middle-class families, they will go down," she said. "I will not sign a bill into law that does not lower costs for middle-class families."

The underlying argument Warren is making is that while voters might pay higher taxes under Medicare for All, that would be more than outweighed by the elimination of healthcare costs like premiums or co-pays. She very pointedly did not say that taxes would go up — a soundbite that could be easily weaponized.

South Bend Mayor Pete Buttigieg seized on Warren's answer and attacked.

"Well, we heard it tonight, a yes or no question that didn't get a yes or no answer," he said.

He later added that the Sanders version of Medicare for All that Warren has endorsed would almost entirely eliminate private insurance, which stands in opposition to what many Americans want from their healthcare: "I don't think the American people are wrong when they say that what they want is a choice."

Public option vs. single-payer

Polls have shown that a public option plan whereby there's a government-run plan that competes with private insurers is more popular than single-payer. A CBS News poll released today found that 59 percent of voters believe that a government-run insurance plan should "compete with private insurance" (as would be the case under a public option), while 32 percent said they would want it to replace private insurance.

While Sanders' Medicare for All bill does not lay out the taxes it would impose, he has floated the idea of a 4-percent tax on all Americans making over $29,000 per year as one way to pay for it, along with taxes on the rich.

It is possible that many families the middle class will pay less under Warren's plan. But without knowing exactly which taxes would be raised and by how much, however, it is impossible to know exactly what the effects would be, as the Washington Post reported last month.

While Warren did not say it, Sanders himself did say that taxes would go up for many Americans.

"I do think it is appropriate to acknowledge that taxes will go up," Sanders said. "They're going to go up significantly for the wealthy. And for virtually everybody, the tax increase they pay will be substantially less, substantially less than what they were paying for premiums and out-of-pocket expenses."

Minnesota Sen. Amy Klobuchar used this as an opening to also attack Warren for not directly making that point herself.

"At least Bernie is being honest here and saying how he's going to pay for this and the taxes are going up," she said. "And I'm sorry, Elizabeth, but you have not said that, and I think we owe it to the American people to tell them where we're going to send the invoice."

Warren, for her part, stuck to her main line of argument, on highlighting total costs: "The problem we got right now is the overall cost of healthcare," she said in responding to Klobuchar.

Former Vice Pres. Joe Biden later added his own input, saying that Warren was being "vague" in her answers.

Wealth tax

The idea of a wealth tax — an idea pitched by both Sanders and Warren — was also the locus of more moderates-versus-Warren arguments. Warren has made her wealth tax one of her cornerstone issues, saying that it would pay for several of her more sweeping plans, like tuition-free public college.

The tenor of this debate was different, however, with the attackers saying they are open to the idea.

"I'm all for a wealth tax. I'm all for just about everything that was just mentioned in these answers," he said. "Let me tell you, though, how this looks from the industrial Midwest where I live: Washington politicians, congressman and senators, saying all the right things, offering the most elegant policy prescriptions, and nothing changes."

Polling shows that a wealth tax is more popular than Medicare for All, and in some polls even gets more support than opposition from Republicans.

Similar to Buttigieg, Klobuchar said she could support a wealth tax, but added that she would rather repeal tax cuts for higher-income Americans passed under Trump.

"It could work. I am open to it. But I want to give a reality check here to Elizabeth, because no one on this stage wants to protect billionaires," she said. "We just have different approaches. Your idea is not the only idea."

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