The New York Post reports that Zohran Mamdani and a slate of allied candidates swept last week's Democratic primaries, and that Democratic leaders and outside experts are now conceding the victory was not simply the product of an affordability pledge. Something else, they say, was driving it. I am not surprised. Slogans are the visible surface of economic frustration; what lies beneath is always more instructive.

Let me state the orthodox objection fairly. One might argue that urban housing costs are a supply problem — a planning failure, a thicket of zoning law — and that no amount of political energy directed at 'affordability' addresses the structural constraint. There is real truth in this. I would not dismiss it. Constraint on the supply side is genuine, and any serious programme must grapple with it.

And yet. When a city the size and wealth of New York cannot house the nurses, teachers, and transit workers upon whom its daily life depends, we are not merely looking at a planning failure. We are looking at a failure of public investment on a scale that compounds over decades. Housing, transit, childcare — these are not luxuries that a prosperous city happens to provide. They are the infrastructure of aggregate demand. When they are inadequate, workers spend more of their income on necessities, save less, consume less, and the city's own economic engine runs below capacity. The micro-prudence of every landlord maximising rent becomes the macro-folly of a city that prices out its own workforce. I described a version of this dynamic long ago; it has not grown less true with age.

What the New York Post's reporting suggests — and I mark this as inference from the headline and lead, not from detailed evidence I can examine — is that the deeper fuel of this political moment was not a policy checklist but an animal spirit of a particular kind: not the entrepreneurial optimism I usually associate with that phrase, but its dark mirror, the collective conviction that the existing arrangements are not working and that someone must act. Animal spirits run in both directions. When private investment in affordable housing will not come because returns are insufficient, and when the state has for years declined to fill the gap, frustration accumulates. Eventually it finds a political expression. That expression arrived last Tuesday.

The policy lesson, if one is wanted, is straightforward enough to state and difficult enough to execute. Public investment in housing — direct construction, land acquisition, long-term subsidy — is not socialism in any sense that should frighten a serious economist. It is what cities and states do when markets produce outcomes that undermine the conditions necessary for markets to function. The question is not whether the state should act, but whether it will act with sufficient scale and speed to meet the underlying demand. A programme that is too small to matter, announced with great fanfare and delivered over twenty years, is not a programme. It is a gesture. And gestures, as New York's voters appear to have concluded, are no longer sufficient.