Cities stood to be among the biggest beneficiaries of a provision of the Affordable Care Act expanding access to Medicaid. The low-income are disproportionately concentrated in urban America. So are major regional medical centers like Grady Memorial Hospital in Atlanta that provide care for and attract the uninsured from far outside of cities. Urban residents also frequently foot the bill for local taxing districts that help pay for this care.

For all these reasons, the Medicaid expansion contained in the law was a no-brainer for big-city mayors: The federal funding promised to cover anew tens of thousands of residents in many cities who had otherwise been turning up in hospitals with no insurance at all.

Some of the country's biggest cities, though -- Atlanta, Miami, Houston, Dallas, Philadelphia -- are so far missing out on these benefits. Governors and state legislatures in their states have rejected the Medicaid expansion, following a Supreme Court ruling that allowed them to do so. The scenario highlights two conflicts: one between Democratic cities and their Republican-leaning state capitals; the other between local officials steeped in the practical reality of governing, and state officials for whom Medicaid opposition has been much more philosophical.

From the former camp, these numbers recently released by the Urban Institute and the Robert Wood Johnson Foundation illustrate the disparate impact of Obamacare in cities benefiting from the Medicaid expansion and those that (for now) are not:

The number of non-elderly poor newly covered in Atlanta under Obamacare would have increased by about 60 percent had Georgia embraced the Medicaid expansion. Instead, it will increase by less than 10 percent. That's a difference of about 46,000 people. In Houston, the state decision not to expand Medicaid will leave about 165,000 people without care who would be eligible otherwise (or if they lived in, say, New Mexico). In Philadelphia, it's about 111,000.

Here is another way to look at the differing impacts:

The share of the population without insurance in Memphis would have declined by about 60 percent if Tennessee were expanding Medicaid. Instead, the uninsured population is projected to decline by about half that.

These numbers underscore a particularly unfortunate irony in places like Texas: Most of the states that have refused the expansion were stingier with Medicaid even before the ACA, meaning that they also stood to benefit the most from the law's higher eligibility standards.

Now adults living just below the poverty line in a city like Houston will be left without any coverage at all. They'll make too much money to be covered by existing Medicaid programs. But they won't make enough to qualify for subsidized plans on an Obamacare exchange.