“Medicare-for-all” is quickly becoming a rallying cry for many Democratic White House hopefuls, but there are growing questions about how to pull off such a dramatic switch to a government-run health care system.

The debate over scrapping private insurers has heated up in recent days since Democratic Sen. Kamala Harris of California, a supporter of “Medicare-for-all,” told CNN’s Jake Tapper, “Who of us has not had that situation, where you’ve got to wait for approval, and the doctor says, well, I don’t know if your insurance company is going to cover this? Let’s eliminate all of that. Let’s move on.”