This leftist populism is a profound error. It has no chance of matching the populist appeal of the right, and it dangerously validates some of the right’s arguments. This only fuels a cynicism that depresses support for the more progressive parts of the left’s program.

But this left tendency has gained from the seeming paralysis of the center. The parties and politicians of the center have become the managers of the status quo in an era when people want change. So, the center — in both its center-right and center-left camps — is marginalized, even despised.

The question is, will this be a temporary phase, perhaps linked to the aftermath of the 2008 financial crisis and Sept. 11, and will politics soon revert to normal, or has a new political age begun?

The party structures on both sides of the Atlantic have their origins in the Industrial Revolution and the debates engendered by that epoch about socialism and capitalism, the market and the state. These parties have endured because the roots they put down were very strong. But now, there are different distinctions than those simply of traditional right and left.