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President Barack Obama made a stunning policy shift on Friday, endorsing "Medicare-for-all" -- a single-payer health system -- for the nation. Most Democrats contending for the 2020 presidential nomination, and many Dems vying for Congressional seats this fall, are backing it, too.

But beware. They're pulling a bait-and-switch. The phrase "Medicare-for-all" sounds as American as apple pie. A new Reuters poll shows 70 percent of Americans respond to it favorably. That's because the public isn't getting the truth about what it means. The actual plan these Democrats are pushing doesn't look anything like Medicare. They're slapping the Medicare label on what would be dangerously inadequate health care.

For starters, it would rip away private health coverage from half of all Americans, including the 157 million who get their insurance the old-fashioned way -- earning it through a job. Conveniently, Democrats are forgetting to tell you that private insurance would be banned under their scheme; employers would be barred from covering workers or their families. Union members and executives who bargained for gold-plated private plans would lose them and have to settle for the same one-size-fits-all public coverage as people who refuse to work at all. Even immigrants here illegally would get the same benefits. What's the point of working?

"Medicare-for-all" is no longer a fringe proposal favored by the extreme left. It's gaining steam. Republicans who failed miserably to communicate a case for repealing and replacing Obamacare cannot make that mistake again. They need to warn voters about the dangers of single-payer health care.

Under "Medicare-for-all" -- the legislation introduced by Senator Bernie Sanders -- Americans would be automatically enrolled in the public program. Kids would be enrolled at birth.

The new scheme would guarantee hospital care, doctors' visits, even dental, vision and long-term care, all provided by Uncle Sam. But that's only until the money runs out. Sanders' bill imposes hard-and-fast dollar caps on how much health care the country can consume yearly. That means limiting mammograms, hip replacements and other procedures. Sanders' bill creates new regional health authorities to curb "overutilization" of care.

Seniors and baby boomers are big losers under "Medicare-for-all." Whenever boomers have to vie with younger people for health resources, they get pushed to the back of the line. In the United Kingdom's single-payer system, boomers are turned away for hip replacements. They're told they have fewer years of life ahead to benefit from costly medical procedures. British women are livid because many are being refused breast reconstruction after lumpectomies and mastectomies.

At least in Britain, people are free to buy private insurance and go outside the government system for care. But that's not true under "Medicare-for-all." You'd be trapped.

Dems backing Sanders' bill point to Medicare's cost efficiencies and say they can be expanded to the whole population. That's ridiculous. Medicare pays only about 88 cents for every dollar of care, shortchanging hospitals and doctors. These providers take the payments because they can shift the unmet costs on their patients with private insurance. But if everyone is on "Medicare-for-all," no cost-shifting is possible. The only alternative is lowering the quality of care -- longer waits, limited access to technology.

Single-payer advocates don't deny it. Stanford economist Victor Fuchs argues in the Journal of the American Medical Association that curbing the use of mammograms, new drugs and diagnostic technologies would make single-payer affordable. In short, go low-tech. But millions of American women have survived breast cancer thanks to high-tech screening and new gene-based therapies. Low-tech medicine would be a death sentence.

The United Kingdom's rock bottom survival rates for breast, lung, ovarian and pancreatic cancer are the result of that low-tech approach. British newspapers are declaring, "Cancer shame as UK survival rates lag behind the rest of the world."

Is that what we want in America?