The cost of housing is making it increasingly difficult for families to move up the economic ladder. Andrew Flowers of FiveThirtyEight reports that 52 percent of renter households below the poverty line spent more than half their income on housing in 2013, up from 42 percent in 1991. One reason is that few households receive government assistance in the form of public housing or rental subsidies. Housing aid is rarely mentioned in presidential campaigns and is perpetually underfunded; about three-quarters of renter families who qualify for aid do not get it because Congress simply has not appropriated enough money.

Another problem is that there is not enough housing where it would do the most good: in places with economic opportunity. Historically, if you were unable to find a good job, you could move to a place where your skills were more in demand. With a more efficient distribution of labor, the states “converged,” and the income gap between poorer states like Mississippi and wealthier states like New York began to narrow. During the past three decades, this convergence has stopped and may even be reversing. The economists Peter Ganong and Daniel Shoag offer an explanation: Thanks to restrictions on land use, we are not building enough homes in areas with strong job markets. As a result, all but the highest paid workers tend to remain where housing is relatively affordable—even if unemployment is high and there is little wage growth.

During this election year, it is important to uphold the American tradition of welcoming newcomers from other nations (Am., 9/19). Americans in economically thriving areas must also welcome citizens from other states, and that means tearing down legal barriers to affordable housing.