Persistent questions about whether she would raise taxes on the middle class to pay for universal health coverage have dominated her campaign in recent weeks. Warren has refused to answer, arguing that it's more important to note that overall costs would fall for nearly everyone but large corporations and the wealthy.
That hasn't quelled the criticism and, recognizing the push for specifics isn't going away, Warren is promising to soon unveil details about how she would cover the costs of what would be a massive new federal entitlement. The release will test Warren's ability to navigate the Democratic primary as she balances the demands of progressives who are open to new taxes against skepticism from moderates who say such levies would doom her in a general election.
"She's trying to thread the needle between the electorate that wants a simple answer and the facts that she knows and that she has to live with at some point down the road," said Jim McDermott, a former Democratic congressman from Washington state who spent most of his career trying to move a "single-payer" plan.
With the first votes just over three months away, Warren could leave many disappointed. If she aligns with Sanders, who acknowledges taxes will have to go up, she could further alarm Democrats worried she's pushing the party too far to the left. If she doesn't, that could alienate progressives who may accuse her plan of not going far enough. And any combination of the two might leave virtually everyone else still confused — wondering how to make the program's eye-popping math work.
That Warren is having to address health care questions on such starkly political terms may recall another, early campaign test she flunked: releasing the results of a DNA test last fall. Meant to quiet critics who questioned her past claims to Native American heritage, the move angered tribal leaders and energized critics like President Donald Trump who still gleefully deride Warren as "Pocahontas."
Warren says that, far from having boxed herself in politically, she's been working on her health care plan for months and still sees it as a winning issue. Her campaign has consulted experts, is reviewing Sanders' funding options on universal coverage going back to his 2016 presidential run and says it will always stay true to Warren's promises that health care costs rise for the rich and big firms while falling for "hard-working families."
One expert Warren's team has consulted is Robert Pollin, a University of Massachusetts Amherst economist who supports Medicare for All and has called for partially helping to pay for it using a sales tax.
"We should all pay something," said Pollin, who is a past donor to both Warren and Sanders but declined to discuss the specifics of his conversations with Warren's campaign. "You're going to get health care with no premiums, no deductibles, no fear of bankruptcy if you have a health emergency."
Warren has refused to commit to the idea of everyone paying a little. But presenting the payment specifics she's promised means necessarily grappling with the possibility of higher overall costs for the program, since making health care free for the patient would encourage people to use more services.
Sara Collins, vice president for coverage and access with the nonpartisan Commonwealth Club, said the key involves changing how the health care tab is divided up among employers, government and individuals.
"The overall growth in spending isn't that great, but it's the 'Who pays for it?' that really changes," said Collins, adding that costs would shift to the federal government, meaning "taxes will likely have to go up."
More pitfalls may emerge as the Warren campaign tries to estimate Medicare for All's cost. Since the final product would have to be approved by Congress, its contents are impossible to predict. A study released last week nonetheless estimated the government would need $2.7 trillion for Medicare for All to be fully implemented next year — more than half the current federal budget.
Sanders' campaign estimated that the universal health coverage plan he first introduced in 2016 would cost $14 trillion over the next decade. His estimates for the current race are far higher, though he now wants to offer more coverage.
Unlike Warren, Sanders has already released payment options, including higher taxes on wealthy Americans and an employee payroll tax of 7.5%. But he's also suggested a 4% "premium" on income that kicks in after the first $29,000 for a family of four — very much affecting the middle class.
Warren could possibly avoid that by imposing co-pay rules or limiting what's covered. Her plan may institute payroll taxes to transfer what employers already spend on employee health care through private insurance to government-run Medicare for All. But that would give federal authorities more control over employee health costs than employers, potentially affecting jobs.
"If your plan for health care involves the perception, even if it's not reality, that you're going to take away something that people have worked very hard to maintain — then it would be very problematic," said Brandon Dillon, former chairman of the Michigan Democratic Party.
Warren's predicament is striking since she emerged as a front-runner alongside former Vice President Joe Biden by proudly "having a plan" for everything but arguably the 2020 race's top issue. She's also spent months deftly floating above questions about paying for her other ambitious proposals, including offering universal child care and tuition-free education at public universities while canceling existing student debt, by proposing a wealth tax on the ultra-rich. That proposal effectively became a piggy bank to cover the costs of her other promises.
The wealth tax won't be enough to pay for Medicare for All, though. Warren's avoidance of the middle-class tax question has helped the issue linger as a political liability — and not just in Washington political circles.
Peter Schweyer, a Democrat in Pennsylvania's House of Representatives who is undecided in the presidential race, called pointed questions of Warren over Medicare for All during last week's presidential debate "really good."
"She'll need to figure out how to respond," Schweyer said.
Associated Press writers David Eggert in Lansing, Mich., and Marc Levy in Harrisburg, Pa., contributed to this report.