Hillary Clinton is pushing back on attempts by her rival for the Democratic nomination, Bernie Sanders, to paint her as the "establishment" candidate.

"I just don't understand what that means," Clinton said in an interview on CNN Thursday afternoon. "He's been in Congress. He's been elected to office a lot longer than I have. I was in the Senate for eight wonderful years representing New York. He's been in the congress for 25, and so I'll let your viewers make their own judgment."

Sanders, who is an independent senator from Vermont, suggested in an MSNBC interview earlier this week that groups like the Human Rights Campaign and Planned Parenthood - both of whom have endorsed Clinton - are "part of the establishment."

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Clinton's initial response during a campaign rally in Burlington, Iowa Wednesday evening was to say she wished the two groups were part of the establishment.

"I wish we weren't fighting all the time to protect women's rights - to protect women's health," she said.

But at the same time as Clinton is seeking to paint Sanders as a member of the establishment, some of her surrogates have argued that Sanders' political identification as a Democratic socialist puts him too far outside the mainstream.

Connecticut Gov. Dan Malloy said, "I think the term socialist doesn't make it easier to win." And Rep. Steve Israel, D-New York, said, "There is a place to carry the socialist banner, there is no question about it, I am not so sure that particularly in swing congressional districts that's the banner you want to be parading."

Clinton has stepped up her attacks on Sanders in recent days, suggesting his foreign policy and health care plans are insufficient. The attacks come as the race in Iowa looks increasingly close. The latest CNN/ORC poll released Thursday showed Sanders leading Clinton in the Hawkeye State, 51 percent to 43 percent.

His campaign used the poll to bolster their argument about Clinton being part of the establishment.

"At a time when Sec. Clinton's lead is evaporating in Iowa we understand why her campaign is panicking and saying absurd things," Sanders' spokesman, Michael Briggs, said in a statement after the poll was released. "The people of Iowa showed extraordinary courage in 2008 by voting for Barack Obama over Hillary Clinton, and many Iowans now understand that it's too late for her brand of establishment politics and establishment economics."