BUILDING AFFORDABLE housing requires local politicians with stiff spines who will fend off predictable and bitter opposition. Those who buckle to that opposition invite a future plagued with problems like San Francisco’s and Seattle’s — gilded playgrounds for the rich where middle-income residents are banished and the poor forced onto the streets.

Wary of that scenario, planners in the Washington region have warned local officials to get busy shifting public funds and amending zoning rules to ensure construction of tens of thousands of additional apartments that fit the budgets of nurses, firefighters and graphic designers, as well as recent college graduates and retiring baby boomers. By continuing to ignore the swelling deficit of affordable housing, they warned, the District and suburban localities will face mounting problems keeping and attracting workers, and risk driving away businesses and employers.

That was a compelling argument for most local elected officials, including District Mayor Muriel E. Bowser, who set a specific target: 12,000 new affordable units by 2025, targeted at families of four earning less than $97,050 a year and single people making less than $68,000. Now comes pushback from Montgomery County Executive Marc Elrich, who says: Not in my backyard.

Ms. Bowser and Mr. Elrich are both liberal Democrats, each of them with large numbers of well-off constituents who will be uneasy with major new housing construction geared toward poor and lower-income residents. But while Ms. Bowser sees the future plainly and is ready to withstand political headwinds to prepare for it, Mr. Elrich, who leads a jurisdiction of more than 1 million people, prefers to engage in magical thinking.

Specifically, he says he would rather boost household incomes in Montgomery than assume so many residents will need moderate- to low-cost housing. He rejects projections and recommendations by the Metropolitan Washington Council of Governments, the regional planning body, that Montgomery County needs to build roughly 23,000 additional affordable units by 2030, more than any other area locality. He termed it “unfair” that Fairfax County, the region’s most populous jurisdiction, is projected to need fewer.

The trouble is that Montgomery, despite broad swaths of affluence, cannot wish away the growing demand for affordable housing, which is based on demographic patterns long underway. Compared to Fairfax and the District, the county has been a laggard for years at attracting businesses and new jobs, in part because of a reputation for policies unfriendly to employers.

Mr. Elrich, a council member for 12 years before he was elected county executive a year ago, has played a part in perpetuating that reputation by standing in opposition to an array of commercial and residential projects. In his current job, he has spoken about attracting more high-paying jobs, but he has not fundamentally altered the county’s trajectory in that regard. In stark contrast to his position, Montgomery’s County Council has unanimously embraced the need for much more affordable housing.

Boosting household wealth is an admirable goal, but pursuing it will not airbrush predictable problems into oblivion.

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