Some of the 2020 Democratic presidential hopefuls are forging ahead with “Medicare-for-all,” but others are taking a more cautious approach.

They’re flagging the political risks of passing a government-run insurance system through Congress and the daunting transition and higher taxes that would follow.

Experts say the debate so far glosses over the enormous challenges of putting in place a single-payer system with the government fully in control of the $3.5 trillion U.S. health care system.

Proponents like Sen. Bernie Sanders, the Vermont independent, hold out the promise of health care as a right, the potential for national savings, and no more copays, deductibles or surprise medical bills.

Among the skeptics — former New York Mayor Michael Bloomberg has said the plan would “bankrupt for us for a very long time.”