Other ideologically driven critics of Sanders-style Medicare for all have been stoking fears about its cost. The conservative Mercatus Center, a George Mason University think tank funded in part by the Koch brothers, has estimated that from 2022 to 2031, total health-care spending in Medicare for all would be a whopping $57.6 trillion and would add $32.6 trillion to the federal budget. Without context, that sounds astronomical. But it leaves out that the United States is already slated to spend nearly $60 trillion in those 10 years on health care—which, it turns out, is actually $2.1 trillion more than under Sanders’s Medicare for all plan. (The Mercatus Center argues those savings would be illusory, because hospitals and doctors would demand higher Medicare rates to make up for lost revenue from private-insurance payments.)

The real obstacle to Sanders’s plan is the public’s expectations. As much as Americans hate insurance companies in general, they want the right to have a love-hate relationship with their own insurer. During the battle over the Affordable Care Act, President Barack Obama promised, “If you like your plan, you can keep it.” When a handful of Americans lost their plans, the backlash was tremendous—even when the cancellations had nothing to do with the new law. The polling data today are clear: When Americans are told they might have to give up their current insurer, fewer than 40 percent support Medicare for all. That’s nowhere near enough to override the entrenched interests in health care.

Read: The coming Democratic drama over Medicare for all

More important, Sanders’s Medicare for all would put almost all private insurance companies out of business—or diminish them to runts. These companies manage more than $1 trillion in revenue per year and cover more than 175 million Americans. For Sanders and his supporters, the prospect of putting nearly all those companies out of business is a major attraction of Medicare for all. But no trillion-dollar industry has ever just rolled over and died. Insurers have experience fighting far less ambitious health reforms—and winning.

If you don’t believe insurers would effectively thwart Sanders’s plan, go to YouTube and look at the old Harry and Louise ads that ran in 1993 and 1994—the last time health insurers felt an existential threat from Washington. Those ads did the impossible, turning widely despised insurance companies into lovable teddy bears that Americans suddenly thought they would miss if Bill Clinton’s health-care-reform plan passed. Ultimately, no congressional committee ever even voted on his proposal. Sanders’s Medicare for all plan could easily suffer the same fate.

The genius of “Medicare for all” is that it explicitly links one of today’s most complicated and challenging policy issues—securing health coverage for all Americans—to the most widely celebrated achievements of Lyndon Johnson’s Great Society. Yet some versions of Medicare for all are hardly ambitious at all.