For decades now, the American National Election Studies survey has asked voters to place themselves on a 7-point scale to identify their feelings about the idea that "there should be a government insurance plan which would cover all medical and hospital expenses" versus the idea that "medical expenses should be paid by individuals and through private insurance plans like Blue Cross."

Respondents are told that an answer of 1 makes them very supportive of the government insurance plan, while an answer of 7 makes them very supportive of the private coverage solution. Here's a chart showing how many people place themselves as 1 to 3 on the scale over time:

If you break this down by demographic group, you'll find that in 2008 most Democrats were supportive of the government plan. So were most people in the bottom third of the income distribution and most black people.

But between the 2008 election and the 2012 election, support for the government insurance plan plummeted. And though it did so in a somewhat polarized way, including a 14 percentage point drop in Republican support, the fall is pretty much across the board. There was a 6-point drop in Democratic support and a 10-point drop in black support.

It used to be that the government plan was more popular outside the South than in the South, but by 2012 only 32 percent of Southerners and 33 percent of non-Southerners supported it. By 2012, the only demographic sub-sample that registered majority support for the government plan was self-identified liberals, with self-identified Democrats coming close at 50 percent support.

One way to interpret this is that it's part of a broad general trend toward more conservative public opinion on tax and spending issues in response to the Obama administration's tax increases.

Alternatively, one could view it as in part a result of the Affordable Care Act reducing public interest in creating a government-run system. With fewer people left uninsured, the idea could seem less compelling. The push for health care expansion in 2009, in other words, may have foreclosed the possibility of a single-payer system.

But of course, all this might change as a result of Bernie Sanders’s political revolution.