Story highlights Bernie Sanders won the support of former Democratic Party Chairman Paul Kirk, but cannot escape questions about his health care plan

Sanders promised again that he would release details of his plan before the Iowa caucuses

Washington (CNN) Bernie Sanders on Thursday stood by his pledge to outline his health care plan before the Iowa caucuses amid criticism from Hillary Clinton and conflicting statements from within the Vermont senator's campaign about whether he will meet his own deadline.

"What this plan does, of course, is end private insurance payments for the American people," Sanders said during a campaign stop at Dartmouth College. "So instead of making a private insurance premium payment, you're now going to make a Medicare premium payment. And what all of the studies indicate is that payment under a Medicare-for-all single-payer system will be significantly less than what middle class families today are paying for health insurance."

Sanders campaign manager Jeff Weaver said as recently as Wednesday that the campaign does not yet have a date for when to release the Medicare-for-all plan.

Asked when he would release details of how his plan would be paid for, Sanders first said, "the truth is we already have a plan," referencing his 2013 proposal for expanding Medicare, but later said, "certainly before Iowa."

Sanders is running neck and neck with Clinton in Iowa, just a few weeks before Democrats head to the caucuses there.

Read More