So the problem is not technological or, from a long-term cost-benefit perspective, financial.

Rather it is the existential challenge to the messy democracy we’ve devised. The hardest part of what lies ahead won’t be deciding whether to construct Eiffel Tower-size sea walls across the Verrazano Narrows and Hell Gate, or overhauling the city’s sewage and storm water system, which spews toxic waste into rivers whenever a couple of inches of rain fall because the sea levels have already risen so much. These are monumental tasks.

But more difficult still will be staring down the pain, dislocation and inequity that promise to upend lives, undo communities and shake assumptions about city life and society. More than requiring the untangling of colossal red tape, saving New York and the whole region for the centuries ahead will become a test of civic unity.

In New York last week to tour the damage, President Obama named Shaun Donovan, his secretary of Housing and Urban Development, a New Yorker and former housing official in the city, to spearhead federal recovery efforts. Mr. Donovan is an obvious choice. But then the president reflexively pledged (and the vice president followed up with the same promise on Sunday) to restore ravaged neighborhoods and homes in Queens and on Staten Island to the way they were before Hurricane Sandy.

That was business as usual, and the last thing the region or the country needs. At this point there’s no logic, politics and sentiment aside, to FEMA simply rebuilding single-family homes on barrier islands like the Rockaways, where they shouldn’t have been built in the first place, and like bowling pins will tumble again after the next hurricane strikes.