If the Federal Reserve is right, the rapid growth that defined the economy of postwar America is over. The central bank has once more lowered long-run expectations, with the US economy of the future projected to grow about half as fast as the economy of the past 70 years. This in turn means a slower increase in our standard of living. It is a threat to the quintessential American notion that every generation will be better off than the previous one. It is also one of the biggest challenges for the next president.

So which party is best placed to address the problem? As a life-long Republican, I believe my party generally has better policies for prosperity, but I have never believed good economic policy is our exclusive prerogative. In fact, I think America’s remarkable postwar growth rests in part on bipartisan commitment to the notion that, as President John Kennedy put it, “a rising tide lifts all boats”.

This makes an emerging debate among the left all the more important: is slow growth the new normal? Or should we focus our efforts on boosting output?