New York -- Hillary Clinton's campaign called on Bernie Sanders to outline how he would cover the cost of his plan to provide universal healthcare to Americans through a single payer, "Medicare-for-all" program.
"From our perspective," said Clinton senior adviser Jake Sullivan on a call with reporters on Wednesday, "the campaign owes an explanation about why it is that they are touting a healthcare plan for which they won't provide any details."
Throughout the course of his campaign, Sanders has advocated for a universal system that would guarantee healthcare "as a right" to all Americans. And with less than three weeks until voters in Iowa gather to cast the first votes, Clinton has blasted his plan as a "risky deal" that could "hurt" middle class families.
Sullivan accused the Sanders campaign of hiding the details because it "does not want to outline what is going to amount to an across-the-board tax hike."
"They've even directly claimed that the new plan wouldn't raise taxes on the middle class," Sullivan said. "We believe that is simply flat out wrong."
Sanders last introduced legislation for a single payer system in 2013 that included a tax increase on individuals and a payroll tax on employers. Michael Briggs, a spokesperson for Sanders, told the Washington Post on Wednesday that the campaign is readying a new proposal but has not determined when it will be released.
On Wednesday morning, in response to the increased pressure from Clinton, Briggs released a fact sheet that detailed how Sanders would pay for various parts of his economic agenda, like making public colleges and universities tuition-free. The fact sheet did not include Sanders' healthcare plan, which Sanders says will ultimately save middle class taxpayers money.
His campaign also distributed a video from 2008 of Clinton decrying Democrats attacking each other over universal healthcare.
"She's attacking me because I support universal health care," Sanders said in an interview on MSNBC. "In 2008, she was attacking Obama because Obama was attacking her because she supported universal health care. I would hope that Secretary Clinton will tell the American people, does she support universal health care?"
In her second bid for the nomination, Clinton has advocated for making changes to the Affordable Care Act in order to lower out-of-pocket costs and prescription drug costs for consumers.
"Secretary Clinton absolutely respects Democrats who support the principles of a single-payer system," Sullivan said. "She believes that many of those people would agree with her that now is not the moment to plunge this country back into a divisive debate over healthcare."
He added: "Our task now is to defend the Affordable Care Act against Republicans who are persistently voting to repeal it."
The back and forth between the two candidates and their respective campaigns also comes as new national and early state polling show Sanders gaining, or overtaking, Clinton. But Clinton aides have declined to say the polls are behind the recent shift in strategy.
"These are issues that were discussed quite aggressively in the very first debate and have been part of the debates ever since," said Brian Fallon, Clinton's national press secretary, on the conference call.