President Obama has flirted with some modest versions of these ideas. During the 2011 negotiations over the debt ceiling, he suggested he’d support a deal that included a higher Medicare age, much to the horror of liberal supporters (like me). And his most recent budget called for, among other things, higher charges to upper-income beneficiaries. But he's never endorsed the radical, wholesale changes conservatives support. And since the election he has made clear his preference for reforms that affect providers, not beneficiaries. He’d agree to reduce what Medicare pays drug companies, for example, but not reduce the medical services the program covers. Obama’s allies have said basically the same thing, only in more emphatic terms. In a joint letter earlier this month, Democratic Senators Tom Harkin and Jay Rockefeller wrote, “We urge you to reject changes to Medicare, Medicaid, and Social Security that would cut benefits, shift costs to states, alter the structure of these critical programs, or force vulnerable populations to bear the burden of deficit reduction efforts.”

These liberals aren’t ignoring fiscal reality. They’re actually making a smart argument about how to balance two priorities—reducing the deficit and protecting the people on Medicare and Medicaid. Contrary to what conservatives say and even many centrists seem to believe, the high cost of Medicare and Medicaid isn’t a by-product of government inefficiency. On the contrary, Medicare historically has held down costs as well as, if not better than, private insurance on a per capita basis. That’s thanks, in part, to the administrative advantages of a centralized government program and Medicare’s enormous power to set prices. Medicaid is cheaper still, to the point where, honestly, it's underfunded. The programs keep getting more expensive, relative to inflation, because medical care keeps getting more expensive—and, in the case of Medicare, because of the increase in the number of people coming on the program. That’s due to a variety of factors: paying too much for services and to the people who provide them; delivering a lot of treatments that are unnecessary, unhelpful, or even harmful; focusing too much on acute treatment when we should be focusing on preventative care and other ways of keeping people healthy.

Solving some of these problems is relatively straightforward, at least on paper. If Medicare is paying too much for a health care service or product, the government can simply insist that the program pay less. But imposing these changes too severely or quickly threatens disruptions: If providers don’t get enough money to cover their costs, they’ll perform fewer services or see fewer patients—sometimes, in ways that make it difficult for people to get care they need. The system can tolerate only so much shock at any one time.

And that’s the easy stuff. When it comes to the more complicated causes of health care inflation—focusing on prevention, shifting to treatments that have more proven effectiveness, improving the quality of care—we are still learning how to mitigate those. If Medicare offers doctors incentives to form cooperative groups, for example, will they respond—and will they become more efficient? If malpractice law changes, will the price of health care actually come down—and will quality actually improve? And so on. On these and other issues, doing too little is a danger, but so is doing too much.