For the past year and a half, of all the proxy battles between "Team Hillary" and "Team Bernie" on the left side of the aisle, no issue has been more repsentative of both how passionate people are or how much each "side" misunderstands the other than the future of the American healthcare system.
"Team Bernie", in essence, consisted of progressives (and Democrats) who believe that while the ACA may have improved things to some degree in some ways, it not only isn't enough long-term, it isn't nearly enough short-term either; the next step (and for many, the only acceptable next step) must be moving the entire U.S. population over to a universal Medicare-style Single Payer system, with everyone in the country being covered through a single, comprehensive healthcare program funded entirely (or nearly entirely) by taxes.
