Former vice president Joe Biden’s presidential campaign, if you listen to conventional wisdom, is on death’s door. He leads in national polls but is coming up no better than third in some Iowa and New Hampshire polls. As Sen. Elizabeth Warren (D-Mass.) rose steadily in the polls it seems to the pundit class that she inevitably would pass Biden nationally. And she could, but first she needs to handle a self-imposed problem: how to pay for Medicare-for-all.

When Sen. Bernie Sanders (I-Vt.) confessed that even he did not have a way to pay for the plan he devised and Warren signed onto, Biden’s team pounced. In a written statement, communications director Kate Bedingfield declared, “It’s alarming that Senator Sanders, who has been up-front for years that Medicare for All would require middle class tax hikes, won’t tell voters ‘right now’ how much more they will pay in taxes because of his plan. If not now, then when?”

Bedingfield went on to make this both an issue of character and of electability. "When you’re running to take on the most dishonest president in American history, Senator Sanders and others who back Medicare for All have to preserve their credibility,” she argued. “Any candidates who would scrap the Affordable Care Act — not protect it and strengthen it, like Joe Biden will — have an obligation to be straight with the American middle class about the tax increases they’d be forced to shoulder while losing the option of employer-sponsored and other private health insurance.”

It is not difficult to figure out who the “others who back Medicare for All” and “any candidates who would scrap the Affordable Act” might be. Biden’s camp is turning up the pressure on Warren as she rummages around for $30 trillion or so to pay for Medicare-for-all, something she has refused to go into detail about in debates. Biden, as well as South Bend, Ind., Mayor Pete Buttigieg and Sen. Amy Klobuchar (D-Minn.), did such a good job at the last debate accusing Warren of hiding the ball that she subsequently promised to come up with a financing scheme. She has not done so yet, although she promised 10 days ago:

It is not clear what “getting close” means but she surely will face a barrage of questions at the next Democratic debate on Nov. 20. She can duck again and say she is “still working on it," but that works only for so long.

Biden’s preemptive attack conveyed two challenges for Warren. First, she is promising to roll back the Affordable Care Act at a time when premiums are going down. She needs to explain the justification for scrapping President Barack Obama’s legacy and do so now. Second, the admonition that candidates have to “preserve their credibility” is aimed at contrasting Warren with the known-commodity Biden. (You know me. I’m not going to double cross you.) Biden has been struggling to convey that he really is a forward-looking candidate but, at times like this, “reliable,” “trustworthy" and “candid” — Biden likes to joke that his gaffes show he speaks his mind — may be the best arguments Biden has, especially to go into a general election race against an incumbent who a large majority of Americans find untrustworthy.

Warren’s got her work cut out for her.

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