In the Thursday CNN poll, Sanders grabbed 51% support among likely Iowa caucus-goers to Clinton's 43%.

"At a time when Sec. Clinton's lead is evaporating in Iowa we understand why her campaign is panicking and saying absurd things," Sanders campaign spokesman Michael Briggs said in a statement. "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."

The poll adds to the trend of a surge for Sanders in the early states of Iowa and New Hampshire over the past few weeks.