The theory here, embraced by a lot of the most prominent liberal bloggers and activists, is that centrist Democrats doomed the party when they blocked liberals in Congress from making good on President Obama’s promise of bold change. Specifically, they refused to adopt a more populist stance toward business and opposed greater stimulus spending and a government-run health care plan. As a result, the thinking goes, frustrated voters rejected the party for its timidity.

There are a few strange things about this argument, even beyond the contention that American voters — 41 percent of whom described themselves as “conservative” this year, compared with 32 percent in 2006 — somehow deem Congress to be insufficiently liberal.

For one thing, many of these same liberal activists were saying something very different in 2006, when Rahm Emanuel, who was then overseeing House campaigns for the party, recruited a slate of less ideological candidates to compete in more conservative districts. Some leading bloggers then — who are now proponents of the Blame the Blue Dogs theory — proclaimed themselves to be against ideological litmus tests, arguing that the most important thing was to choose candidates who could actually win.