have health insurance. >> reporter: democrat mindy messmer is campaigning for votes in new hampshire's first district. she argues single-payer health care will cut down on high out-of-pocket costs. >> medicare for all is a system that already works. if we can expand is so everyone has access, that would be most beneficial to everyone. >> reporter: the health care for all idea bernie sanders promoted two years ago is gaining steam with democratic candidates across the country. >> i haven't spoken to one person who does not agree that medicare for all is a good plan. >> reporter: but cost is a big unknown. according to one independent group's estimate, the current trajectory of health care costs is unsustainable, rising faster than wages. at the same time, the price tag for a single-payer system would be $2.5 trillion a year. >> health care is one of those issues here that can really bankrupt our nation. >> reporter: voters will have their say on an issue that has divided the nation on...