John Podesta, Hillary Clinton's campaign chairman, said that Sen. Bernie Sanders' (I., Vt.) health care proposal "sucks" and implied that Democratic primary voters live in a "leftie alternative universe" on that issue, according to newly released hacked emails.

Judd Legum, the editor-in-chief of ThinkProgress, wrote to Podesta on January 13 that people were responding negatively to Clinton's criticism of Sanders' single-payer health care proposal.

"Not sure how it's playing out on your end but having been seeing a lot of negative stuff online about the single payer hit on Bernie," Legum wrote. "See it being fit into the she's dishonest/will say anything to win frame. So I just wanted to make sure you were cognizant of that."

"Thx," Podesta responded, "His actual proposal sucks, but we live in a leftie alternative universe."

The emails were released by WikiLeaks after a hack of Podesta's personal email account. The U.S. intelligence community has accused Russia of hacking U.S. political institutions in order to influence the presidential election.

Hillary Clinton has publicly opposed Sanders' plan, which would create a federally administered single-payer health care program. However, she has praised aspects of single-payer systems in closed-door speeches, saying that they lower costs.

"If you look at countries that are comparable, like Switzerland or Germany, for example, they have mixed systems," Clinton said in 2013. "They don't just have a single-payer system, but they have very clear controls over budgeting and accountability."

"If you look at the single-payer systems, like Scandinavia, Canada, and elsewhere, they can get costs down because, you know, although their care, according to statistics, overall is as good or better on primary care, in particular, they do impose things like waiting times, you know," Clinton said.

Sanders' single-payer proposal would cover impatient and outpatient care, preventive and emergency care, primary and specialty care, long-term and palliative care, vision, hearing and oral health care, mental and substance abuse services, prescription medication and medical equipment, supplies, diagnostics and treatments.

According to a report by the Tax Policy Center, such a plan would increase public and private health care spending by $5.5 trillion over 10 years.

The Clinton campaign did not respond to requests for comment.