WASHINGTON (AP) — 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."