Elizabeth Warren's campaign is looking at ways to finance her vision for "Medicare for all" after facing multiple attacks from rival Democrats on the debate stage Tuesday night about whether she'd raise taxes.

"She's reviewing the revenue options suggested by the 2016 Bernie campaign along with other revenue options. But she will only support pay-fors that meet the principles she has laid out in multiple debates," a Warren campaign aide told CNN Wednesday.

Warren is a co-sponsor of the Medicare for All Act, a bill long championed by Democratic presidential rival Bernie Sanders. The bill does not contain a funding mechanism, but Sanders has acknowledged that the reform would mean raising middle-class taxes. Warren said during the debate Tuesday that if elected she would only sign a bill into law that lowered costs on the middle class but avoided answering several direct questions about whether she would raise taxes.

Under the Medicare for All proposal, Medicare coverage would become more extensive than it is now. It would pay for emergency surgery, nursing home care, prescription drugs, mental health, dental, and eye care, all without co-pays and regardless of citizenship.

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An Urban Institute analysis released Wednesday found that to deliver such a plan the federal government would need to increase its spending by $34 trillion in a decade and that overall national health spending would rise $7 trillion compared to current law. In total, national health spending would reach $59 trillion under the Medicare for All plan.

Sanders has said that his plan would cause taxes to go up on the middle class, but that would replace the healthcare premiums they and their employers pay now under private health insurance. Warren has dodged the tax question in every debate, stressing that "costs" would go down.

"Costs will go up for the wealthy and for big corporations, and, for hard-working middle-class families, costs will go down," Warren said.

But her Democratic rivals pressed her repeatedly on the issue during the debate, as have voters on the campaign trail. Warren's tag line is that she “has a plan for that,” referring to the fact that she has released a multitude of detailed policy proposals, from universal child care to universal free public college, which would be funded through a wealth tax. On healthcare, however, she has said only that she is "with Bernie" on Medicare for All.

"Your signature, senator, is to have a plan for everything. Except this," said South Bend, Indiana, Mayor Pete Buttigieg. "No plan has been laid out to explain how a multitrillion-dollar hole in this Medicare for All plan that Sen. Warren is putting forward is supposed to get filled in."

"The difference between a plan and a pipe dream is something that you can actually get done," said Sen. Amy Klobuchar of Minnesota.

And Democratic front-runner Joe Biden raised the issue again Wednesday.

"She’s going to have to tell the truth, or a question will be raised about whether she’s going to be candid and honest with the American people,” Biden said.