Sen. Kirstin Gillibrand of New York, another co-sponsor of Sanders's bill, stresses this approach. "I can go to anywhere in this country and say, 'Why not have a not-for-profit public option that competes with your insurer charging you too much money?' " Gillibrand said Monday during a Washington Post Live event.

Even Sen. Elizabeth Warren of Massachusetts, who declared "I'm with Bernie on Medicare-for-all" at the first Democratic debate, has given herself wiggle room, saying that "there are a lot of different pathways" to achieving the goal of the Sanders bill.

Sanders himself is emphasizing his continued allegiance to a sweeping version of Medicare-for-all. That shows, he suggests, that he is the only candidate who can be trusted to fight for real change.

His campaign argues that allowing private insurance to remain, with all its inequities and privileges, would only perpetuate a tiered health-care system.

"The moment a person has to open their wallet to get health care in America is the moment that some people will be denied that right," said Ari Rabin-Havt, chief of staff for Sanders's campaign. "Anyone supporting plans that would leave millions without even basic coverage cannot claim to be standing for health care as a right."