A plurality of Americans support “Medicare for All”, legislation endorsed by Bernie Sanders and other Democrats that would establish a universal single-payer health care system in the U.S. At least they do until they find out what“single-payer” really means.

A recent AP poll found that 39 percent support and 33 oppose replacing the current private health insurance system in the U.S. with a single government-run and taxpayer-funded plan like Medicare for all Americans that would cover medical, dental, vision, and long-term care services. (Another 26 percent neither support nor oppose the change.)

But the same percentage (39 percent) opposed single-payer when it was found that it would cause their own taxes to increase or they’d need to give up other coverage, like health insurance provided by their employers. In both cases, about 4 out of 10 flipped to opposition when they discovered that caveat.

Even higher numbers opposed the plan if it would lead to longer wait-times for non-emergency medical services (47 percent) or if it took longer for new drugs and treatments to e available (51 percent).

“People say they believe in a principle, but when you describe the policy, it often loses support because they don’t like that there are side effects,” said Robert Blendon, a professor who tracks public opinion on health care at the Harvard T.H. Chan School of Public Health.

So what exactly would an American version of single-payer plan look like?

A single-payer system is one in which health-care providers are paid for their services by the government rather than by private insurers. Every year since 2003, Democrats in Congress have introduced H.R.676, the Expanded & Improved Medicare For All Act. The key provisions are that it would prohibit private health insurers from selling health insurance coverage that duplicates the benefits provided under the legislation and that it would raise taxes, including payroll taxes, to pay for the extended coverage.

Not surprisingly, the legislation is vague on how much taxes would be raised, saying only that the increase in payroll taxes would be “modest.” But according to the National Institute for Health Care Reform, a national single-payer system would require a payroll tax of 11.7 percent. That means a family earning$50,000 a year would have to pay $5,850 in taxes for health care.

And even that would not be enough to cover all the costs of health care. Even after all the new taxes proposed in Bernie Sanders plan (about $675 billion), the government would still fall $599 billion short of what the country actually spent on health care in 2013.

It’s hardly surprising, then, that when Americans discover the side effects of the single-payer system — higher taxes, fewer choices, longer wait times for treatment —they start to feel a bit queasy.