Peter Beinart is out with a major new argument in The Daily Beast about what the political future might hold in store for us. The headline writer calls it “The Rise of the New New Left,” and it begins by citing the recent victory of liberal populist Bill de Blasio in New York’s mayoral primary. “The deeper you look,” Beinart writes, “the stronger the evidence that de Blasio’s victory is an omen of what may be the defining story of America’s next political era: the challenge, to both parties, from the left.”

The argument is generational: that the class of politicians who govern us now take for granted that our ideological debates take place between the goalposts of Reaganism and Clintonism—as manifested not least in the case of Barack Hussein Obama....

Beinart’s generational argument is deterministic. It’s not about what the defining argument of the future will be. Young people’s ideological outlook seems to him already settled—leftward. That’s far too simple and optimistic.

For one thing it assumes that political dynamics are linear—since the trends tend this way now, they will only tend that way more so in the future. It thus leaves out an awful set of variables that complicates any narrative of progress.

For one thing, he assumes that America has a democracy.

But consider the counter-evidence against that, of which many of you are aware. Thanks to partisan gerrymandering by power-hungry Republicans (remember the counsel to a Texas representative who bragged in a 2003 e-mail to colleagues that they’d fixed it for Republicans to “assure that Republicans keep the House no matter the national mood”), our House of Representatives is, in fact, far from representative. You can’t repeat it often enough: when Barack Obama wins the state of Pennsylvania by five points but the delegation Pennsylvania returns to the House of Representatives contains thirteen Republicans and only five Democrats—well, poll numbers aren’t counting for very much, are they?...