Democratic presidential candidate Bernie Sanders peaks at Northstar Elementary School in Knoxville, Iowa, last month. (AP Photo/Andrew Harnik)

Presidential hopeful Bernie Sanders, who’s been taking flak from his Democratic rival Hillary Clinton over his call for universal health care, expressed frustration Wednesday night with those “who want to demagogue the issue.”

Sanders is advocating moving to a single-payer health-care system under which all Americans would be enrolled in Medicare, and private insurance would become a thing of the past. The Vermont senator introduced legislation with that aim in 2013 and has said he is working on an updated version as a presidential candidate.

In recent days, as the Democratic race has tightened, Clinton and her surrogates have called Sanders’s approach risky, suggested such a plan could be undermined by Republican governors and criticized the senator for not sharing the particulars of how he would pay for an updated plan.

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Appearing Wednesday night on MSNBC’s “All In with Chris Hayes,” Sanders sought to rebut those criticisms, saying that he has been “a little bit disturbed that Secretary Clinton and her team there keep suggesting that it would not apply in Republican states.”

“That’s just not accurate,” Sanders said, explaining that what he is advocating would be a “50-state program” that GOP governors could not block in their states.

Sanders also pushed back against critics of his 2013 bill, which included an across-the-board tax increase to fund the program.

He argued that under a “Medicare for all” system, the average family would actually save about $5,000 a year because they would no longer be paying private insurance premiums, deductibles or co-payments -- more than offsetting the cost of the tax increase.

[With Iowa caucuses looming, Sanders still has some major policy proposals to unveil]

“If you want to demagogue the issue, you can say, ‘Oh, he’s raising taxes,’ but then you’ve got to make it clear that we’re saving people substantial sums of money,” Sanders said.

Asked by Hayes if he thinks Clinton is being a demagogue on the issue, Sanders paused before answering.

“What she is forgetting to talk about is the substantial sum of money we save when people do not pay private health insurance,” he said.

Sanders’s MSNBC appearance followed a day of back-and-forth on the issue between the two leading Democratic campaigns.

Earlier Wednesday, during a conference call with reporters, Clinton spokesman Brian Fallon said earlier versions of Sanders’s single-payer plan called for “a sweeping tax increase,” and he said it is “alarming” that Sanders has not spelled out how he intends to pay for the updated version.

Prior to the conference call, Sanders’s campaign released a list of several other major initiatives that Sanders has proposed as a presidential candidate, along with an explanation of how he would finance them. The health-care plan was not included.

“The Sanders campaign owes an explanation,” said Jake Sullivan, Clinton’s policy director, who suggested Sanders’s updated plan might call for “a massive across-the-board tax hike.”

For its part, the Sanders campaign sought Wednesday to highlight Clinton’s past support for universal health care, an idea that is broadly popular among Democrats.

Sanders’s team released a 1993 photograph of Clinton and Sanders, when she was first lady and he was a congressman, taken on a flight to a health-care forum at Dartmouth University.

A note written by Clinton under the photo reads:  "To Bernie Sanders, with thanks for your commitment to real health care access for all Americans and best wishes - Hillary Rodham Clinton.”

The Sanders’s campaign also shared a video Wednesday from the 2008 presidential race in which Clinton chided her then-primary rival Barack Obama for criticizing her efforts to usher in universal health care.

During his MSNBC appearance, Sanders acknowledged that, given the current political realities in Washington, he would not likely have the votes to push a single-payer system through Congress as his first order of business as president.

“No one has ever heard me say, ‘First day in office, we’ve got single payer,’” Sanders said, characterizing his plan as “the vision we must strive to.”