It would be senseless to replace employer-based coverage with an expensive one-size-fits-all system that couldn’t handle treatments of the future.

My 93-year-old father recently came home from the hospital proudly harboring a life-saving $50,000 aortic valve paid for by Medicare, though he rode home in a wheelchair that Medicare didn’t pay for. This gap in services is growing, as Medicare struggles to cover emerging technologies that are not one-size-fits all while at the same time continuing to provide basic care. If Medicare is converted to single-payer or Medicare for all, as Sen. Bernie Sanders of Vermont proposes, tens of millions  more patients will be added to an already faltering system, and the gap between the promise of care and actual care delivered will widen.

More: Canadian doctor to U.S.: Try single-payer health care instead of trashing it

More: On health reform, forget politicians. What do doctors and patients want?

Single-payer is the ultimate one-size-fits-all health care promise. Consider Canada, our single-payer neighbor to the north. One of my patients was visiting Toronto several years ago when he developed worsening angina requiring a cardiac stent. He was placed on a several-week waiting line before giving up and returning home for the procedure. The waiting-your-turn problem has only gotten worse since then. In 2016, the Fraser Institute found a median 20-week wait in Canada between a generalist’s referral and the time the patient actually received a definitive test or treatment/procedure from a specialist.

Americans already face a wasteful health care system with inadequate access to care. The Commonwealth Fund ranked us last among 11 wealthy nations this summer. But unlike Canada, we will never tolerate such long waiting lines, which is one of the reasons single-payer will never work here.

Despite growing problems in access and cost, most Americans don’t want change to jeopardize what works. A 2016 Gallup Poll revealed that 65% of Americans are happy with the way the healthcare system works for them. The backbone of our system is employer-based health insurance. Some 170 million Americans rely on coverage at their job, and employers receive an incentive to offer it in the form of a tax deduction.

More than 55 million Americans are covered by…