Progressive urbanists and Ben Carson, President Donald Trump's conservative Secretary of Housing and Urban Development (HUD), hardly seem like bosom buddies. That makes Carson's embrace of a core item on the progressives' wish list all the more surprising.

In August, Carson announced that he would be revising Obama-era HUD regulations that required local governments to perform extensive (and expensive) studies of how concentrated their neighborhoods were along class and racial lines, and then come up with plans to remedy the housing segregation they found. In their place, Carson wanted HUD to issue new rules that would put the emphasis not on integrating housing but on building new housing, period. For Carson, that means cracking down on byzantine local zoning codes.

"I want to encourage the development of mixed-income multifamily dwellings all over the place," Carson told The Wall Street Journal. "I would incentivize people who really would like to get a nice juicy government grant" to pursue zoning reform.

Such comments could well have been taken from the script of policy wonks who have rightly identified land-use regulations as the chief cause of staggeringly high housing costs in booming cities such as San Francisco, New York, and Seattle.

A flurry of likeminded proposals from across the political spectrum followed Carson's announcement. In September, progressive Sen. Elizabeth Warren (D–Mass.) introduced a bill that would tie federal infrastructure grants to local zoning reforms. The more market-oriented Niskanen Center also proposed conditioning federal funding to states on meeting housing production quotas. All of these proposals, of course, feature Washington meddling in local affairs.

Despite this newfound enthusiasm for looser zoning regulations, however, Carson's comments have not yet translated into concrete policy action.

That could be because the Trump administration is not all that interested in lowering the cost of housing in big blue cities. A more likely explanation is that there's honestly very little the feds can do to convince suburban "NIMBY"s—people who don't want new development in their neighborhoods—and city-dwelling anti-gentrification activists to accept a large apartment building at the end of their tidy, expensive block.

HUD can't tell local governments what zoning regulations to adopt, and the agency can attach only so many strings to federal housing funds. Carson's comments—which reflect a growing, pan-ideological consensus that the best cure for the nation's urban housing shortage is for cities to allow the construction of more housing—are encouraging. But as with most urban policy, the real action will have to start at the bottom.