Every health care proposal from the right and the left includes some form of implicit rationing device. Mr. Ryan’s plan, on the Republican side, would keep spending on Medicare under 4.75 percent of the nation’s output until 2050 by giving older adults born after 1958 a dollop of money to buy their own insurance, forcing many to choose cheaper plans or fewer procedures.

The president’s health care reform encourages rationing, too, by levying a tax on “Cadillac” insurance plans, and in turn pushing employers to seek cheaper options and lower costs. It creates an advisory board to cut costs from Medicare if spending rises above a set rate. And it finances an institute to evaluate which therapies are most clinically effective. Careful to avoid political blowback, the president’s plan forbids Medicare to base its reimbursement decisions on the institute’s findings.

But neither initiative seems likely to solve our health care financing squeeze over the long term. The cuts proposed by Mr. Ryan — shifting the risk of health care inflation onto the shoulders of older adults — are certainly drastic. They also seem politically unfeasible. Under Mr. Ryan’s most recent proposals, in 2030 Medicare would spend $2,200 less in today’s money on each new enrollee than under the most likely outcome envisioned by the Congressional Budget Office based on current policies. By 2050, it would pay $8,000 less. Voters seem to think that might be too drastic a cut.

The president’s plan was more about offering health insurance to all, to end our Dickensian system of rationing by income, than long-term cost control. Savings mandated by the Affordable Care Act over the next 10 years will be difficult to maintain beyond that.

It puts a lot of faith on eliminating waste, with potentially large savings. David Cutler, a health economist at Harvard, argues that a third of our health care dollars go to therapies that do not improve our health. A lot of that waste could be slashed simply by no longer paying providers a fee for each service, whether we need it or not, and paying them instead to keep us healthy.

Going after waste seems sensible in a health care system that costs more than almost any other in the developed world, yet delivers lower-quality care. But savings from waste tend to be hard to achieve. Even with the Affordable Care Act in place, federal health spending will eat up almost twice as much of this nation’s economic product in 2037 as it does today, according to the budget office.

While it is reasonable for politicians to shy away from rationing — especially when voters believe no expense should be spared to save a human life — if the experience of other countries serves as precedent, they will probably get there sooner or later. In Britain, the National Institute for Health and Clinical Excellence determines what therapies will be covered by the National Health Service. It generally recommends against paying for a therapy that costs more than $31,000 to $47,000 for each year of life gained, adjusted for quality.