Next week, 20 Democratic presidential hopefuls will gather in Miami for their first debate. One issue is sure to dominate the discussion – "Medicare-for-all."

The promise of free, government-run health care has become quite popular among Democrats since Sen. Bernie Sanders, I-Vt., made it a major plank of his 2016 presidential campaign. Four of his rivals for the Democratic nomination have co-sponsored his "Medicare-for-all" legislation. Several others have expressed support for something like it.

Democrats may say they want "Medicare-for-all." But multiple recent polls show they have no idea what "Medicare-for-all" would mean for them – or for the country.

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Two "Medicare-for-all" bills have been introduced in Congress – one by Sanders in the upper chamber, and the other by Rep. Pramila Jayapal, D-Wash., in the House. They're virtually identical. Both would create a new government-run health plan that eventually provided health coverage to every resident of the United States, citizen and non-citizen alike.

That coverage would be comprehensive – everything from primary care, prescription drugs, and surgery to dental, vision, and long-term care.

Sanders and Jayapal have been happy to tout their promise of free care. But they've been a little less forthcoming about the fact that their bills would effectively outlaw private health insurance.

That caginess may explain why two-thirds of Democrats erroneously think people with employer-sponsored insurance would be able to keep the plans they currently have under "Medicare-for-all," according to a Kaiser Family Foundation poll out this week. Almost two-thirds wrongly believe that those who purchase insurance on the individual market will be able to maintain their coverage in Bernie's brave new health care world.

Nearly four in 10 Democratic voters incorrectly believe that private insurers would remain the primary providers of health coverage under "Medicare-for-all."

The Kaiser poll is not an outlier. A separate survey released earlier this week found that 73 percent of Democrats thought "Medicare-for-all" would simply allow anyone who wanted to buy into Medicare to do so -- rather than a compulsory national insurance scheme that would force people off their private coverage.

Outlawing private insurance would have serious repercussions. About 180 million people have employer-sponsored insurance. About 52 million buy coverage directly from insurers. And about 22 million seniors have privately administered Medicare Advantage policies. "Medicare-for-all" would end these coverage arrangements -- and dump everyone into the new, one-size-fits-all government-run plan.

Additionally, eliminating private coverage would put about a million people in the insurance industry out of work -- something Jayapal freely admits.

Canada's single-payer system bans private insurance for anything the government covers, just as "Medicare-for-all" would. Consequently, Canadian patients get care on the government's timetable, not their own -- if they're able to get care at all.

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Last year, Canadians were waiting for nearly 1.1 million procedures, according to the Vancouver-based Fraser Institute. Assuming one patient per procedure, nearly 3 percent of the country's population was on a waiting list last year. The median wait between referral by a general practitioner and treatment by a specialist was just under 20 weeks. Patients in need of orthopedic surgery faced a median wait of almost 10 months!

Democratic voters have said that health care is the number one issue they want to hear their party's presidential candidates talk about. They should pay close attention. They may be shocked by what they find out.

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