Just after the law was passed in 2010, fully 74 percent of moderate and conservative Democrats supported the federal law making changes to the health-care system. But just 46 percent express support in the new poll, down 11 points in the past year. Liberal Democrats, by contrast, have continued to support the law at very high levels – 78 percent in the latest survey. Among the public at large, 42 percent support and 49 percent oppose the law, retreating from an even split at 47 percent apiece last July.

The shift among the Democratic party’s large swath in the ideological middle is driving an overall drop in party support for the legislation: Just 58 percent of Democrats now support the law, down from 68 percent last year and the lowest since the law was enacted in 2010. This broader drop mirrors tracking surveys by the non-partisan Kaiser Family Foundation and Fox News polls, both of which found Democratic support falling earlier this year.