The nation’s largest cities and metropolitan areas — home to a majority of Democratic voters — are at the forefront of the party’s most vexing racial, ethnic and class conflicts.

Last week, in an essay for CityLab, Richard Florida, a professor of urban planning at the University of Toronto, described how housing costs are driving the growing division between upwardly and downwardly mobile populations within Democratic ranks:

The rise in housing inequality brings us face to face with a central paradox of today’s increasingly urbanized form of capitalism. The clustering of talent, industry, investment, and other economic assets in small parts of cities and metropolitan areas is at once the main engine of economic growth and the biggest driver of inequality. The ability to buy and own housing, much more than income or any other source of wealth, is a significant factor in the growing divides between the economy’s winners and losers.

Allies on Election Day, the two wings of the Democratic Party are growing further estranged in other aspects of their lives, driven apart by the movement of advantaged and disadvantaged populations within and between cities. These demographic patterns exacerbate intraparty tensions.

Florida, writing with Benjamin Schneider of CityLab, expands on this point:

While the advantaged members of the knowledge, professional, and creative class have enough money left over even after paying the cost of housing in these cities, it’s the less-well-paid members of the service and working classes who get the short end of the stick, with not nearly enough left over to afford the basic necessities of life. They are either pushed to the periphery of these places or pushed out altogether.

The competition for housing between rich and poor has become a critically important and divisive issue in urban America.

“The state of housing affordability in the expensive coastal metros is driving a wedge between two factions of the American left,” Issi Romem, a fellow at the Terner Center for Housing Innovation at the University of California, Berkeley, wrote in an email to me.