Now, the left vociferously disagrees with the median voter theorem, which holds that in electoral systems like ours the winner will be the candidate who comes closest to the center of the ideological spectrum. Against this assumption, the left points to the remarkable success of the Republican Party in winning elections by running base-mobilization campaigns that explicitly flee from the center. George W. Bush tried this in 2004, and the strategy worked. And of course, Trump prevailed in 2016 after a much more extreme version of the same approach. The left insists that the Democrats will enjoy the same kind of success if they abandon their centrist caution and embrace a full-throated democratic socialist agenda.

Yet as a recent comprehensive Economist/YouGov poll makes clear, the numbers just aren’t there. When nearly 1,500 respondents of various partisan commitments were asked about Democratic ideology, a plurality of them (40 percent) pronounced it too liberal with only 11 percent declaring it not liberal enough. (Twenty-six percent consider the ideological positioning of the party to be about right.) When respondents were asked a parallel question about Republicans, a slightly smaller share (35 percent) declared the party too conservative, while 19 percent asserted that it wasn’t conservative enough. (Twenty percent consider the GOP’s degree of conservatism to be about right.)