Elizabeth Warren's Medicare-for-all plan: How do the numbers add up?

Democratic presidential candidate and Massachusetts Sen. Elizabeth Warren has repeatedly come under fire for dodging questions about how she will pay for her policies, especially Medicare-for-all.

"Late Show" host Stephen Colbert grilled Warren on Tuesday about how Medicare-for-all would affect America's middle class, the same day that a Wall Street Journal/NBC News poll showed that she is rising in the wide 2020 field.

Two separate studies estimate that a Medicare-for-all plan like the one Warren supports — which originated with her 2020 rival Sen. Bernie Sanders — would raise federal health spending by roughly $32 trillion over a decade. And there's no guarantee that overall health spending would go down, even as most people's taxes go up in order to offset the costs of health care to the government.

Warren tried to shift the focus when asked about funding Medicare-for-all at the Democratic debate on Sept. 12, as she did in her exchange with Colbert.

"Hard-working middle-class families are going to see their costs go down," Warren told Colbert.

"But will their taxes go up?" Colbert pressed.

"But here’s the thing —" Warren said.

"No, but here's the thing," Colbert said. "I've listened to these answers a few times before, and I just want to make a parallel suggestion for you about how you may defend the middle-class taxes that perhaps you're not mentioning."

People are noticing Warren's vagueness. Washington Post opinion writer Jennifer Rubin called out the senator on Wednesday for lacking details.

"Warren's brand is truth-telling about the rich and powerful, but you simply cannot get the rich and big corporations to pay for all of it. ... When she says the 'rich' will pay more, who does she think is 'rich'?" Rubin wrote.

Warren has a plan to tax wealth that will raise $2.75 trillion over 10 years according to her website. But the candidate has already said that money would go toward universal childcare or eliminating student debt -- or both.

Meanwhile, analysts are crunching the numbers on Medicare-for-all. The Committee for a Responsible Federal Budget found that "financing a $30 trillion program would require the equivalent of tripling payroll taxes or more than doubling all other taxes."

Warren is trailing only one other candidate, former Vice President Joe Biden, in a WSJ/NBC News poll released Tuesday. She was favored by 25 percent of registered voters polled, behind Biden's 31 percent. Meanwhile, Sanders, who is behind many of the same policies that Warren touts, totaled14 percent.

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Both figures for Warren and Biden are increases from July, when Warren polled at 19 percent and Biden at 26 percent.

FOX Business' inquiry to the Warren campaign was not returned at the time of publication.

FOX Business' Paul Conner contributed to this report.