Democratic candidates who endorsed Medicare for All did significantly worse than those who did not. The estimated coefficient of -4.6 indicates that support for Medicare for All cost Democratic candidates in these competitive districts almost five points of vote margin — a substantial effect in a close election.

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Polling data indicates why single-payer might be a liability. At first glance, Medicare-for-all does poll pretty well: 56 percent approval and 41 percent disapproval, according to the most recent Kaiser Family Foundation survey. It could be aided by some misconceptions, though: More than half of people, for example, think they’d be able to keep their health insurance plan under the single-payer system. (Under Sanders’s bill, they would not; most private insurance would be prohibited after the four-year transition period.)

Polling data indicates why single-payer might be a liability. At first glance, Medicare-for-all does poll pretty well: 56 percent approval and 41 percent disapproval, according to the most recent Kaiser Family Foundation survey. It could be aided by some misconceptions, though: More than half of people, for example, think they’d be able to keep their health insurance plan under the single-payer system. (Under Sanders’s bill, they would not; most private insurance would be prohibited after the four-year transition period.)

But public opinion hinges on how you talk about the issue. Support dropped from 56 percent to 37 percent when voters were told the proposal would eliminate private insurance companies or raise taxes for most Americans. (Support correspondingly surged when voters heard the strongest talking points in favor of the proposal: universal coverage and lower health care costs.)