he recent Democratic primary debates in Detroit made at least one thing clear: The party exclusively responsible for passing the Affordable Care Act is now waging political warfare over whether to reform it or eliminate it. Senator Bernie Sanders was loud but not lonely in advocating “Medicare for all,” which would supplant the A.C.A. with a single-payer system and virtually abolish private employer-based health insurance. His predictable answer to who will fund its high price is apparently the 1 percent who need to pay their fair share.

But there is another 1 percent, and they are not the privileged ones you’re thinking of. They are the roughly 1 percent of Medicare patients who have end-stage renal disease and cost the system $34 billion every year. No matter how rich or poor, young or old, Medicare kidney patients are guaranteed treatment mostly paid for by American taxpayers.

The product of vigorous lobbying and minimal deliberation, this one-disease carve-out that Congress passed in 1972 exemplifies the highly politicized patchwork design of the American health care system and its scandalous lack of universal coverage and adequate cost controls.

Anyone with a sense of compassion can applaud saving three-quarters of a million Americans with failing kidneys from death each year. But this program is exorbitantly expensive, and preventive therapies and other effective treatments can be made available at lower costs. It enriches two for-profit companies that control about 70 percent of the dialysis market. It has created perverse incentives for health care providers to supply too many patients with dialysis while devoting scant resources to preventing end-stage kidney disease and providing more kidneys for transplants.