Fifty years ago last week, an assassin’s bullet claimed the life of the Rev. Martin Luther King Jr., and Washington, among other cities, erupted in violent protest.

Fifty years ago this week, the House, galvanized — or embarrassed, or scared — by the crisis, passed the much-postponed Civil Rights Act of 1968, better known as the Fair Housing Act.

In his April 11, 1968, signing statement, President Lyndon B. Johnson alluded to the 1964 and 1965 laws that outlawed racial discrimination in employment, public accommodations and voting rights, and declared that the measure filled one of the biggest remaining gaps in the new structure of justice.

“Fair housing for all — all human beings who live in this country — is now a part of the American way of life,”Johnson said.

Is it? There has unquestionably been progress. Between 1970 and 2010, the average U.S. metropolitan area’s “dissimilarity index,” a widely used measure of segregation between blacks and whites, declined from 78 to 60, according to sociologists Jacob S. Rugh of Brigham Young University and Douglas S. Massey of Princeton University: To achieve an even racial distribution would have required relocating 60 percent of an area’s African Americans in 2010, as opposed to 78 percent 40 years earlier.

That’s a 23 percent improvement. The United States as a whole is approaching a level of black-white residential segregation that researchers customarily consider “moderate,” and in places such as Blacksburg, Va., or Fort Collins, Colo., housing segregation is in the “low” range, as Massey notes in a review of the data soon to be published in the Journal of Catholic Social Thought.

Nevertheless, black Americans remain far more likely than others to be concentrated racially and isolated geographically, Massey reports. For blacks, nine of the 10 most segregated metropolitan areas are northern cities such as Detroit, Cleveland, Chicago and Philadelphia. Their average dissimilarity index stands at 76, down only slightly from 84 in 1970. These figures do not capture the various deprivations, in transportation, employment and education, that go along with ghettoization, but those are very real, too.

Persistent racial isolation does not result only from natural demographic processes, or private prejudice — though both have played a part. Rather, it is to a large degree a legacy of conscious federal actions that helped ghettoize blacks as they migrated from south to north in the mid-20th century.

When the Roosevelt administration bailed out the housing industry during the Great Depression, it did so on a discriminatory basis, steering Federal Housing Administration subsidies to whites-only neighborhoods, purportedly to avoid the property devaluation that black residents caused. When the federal government built housing for World War II defense plant workers, it did so on a segregated basis. FHA and GI Bill housing benefits also favored white suburbs after the war.

The Fair Housing Act represented a federal promise not only to prevent new discrimination but also to reverse damage Washington itself did.

It has been more successful at the former task than the latter. Overt racial bias in renting and selling homes — of the kind for which the Justice Department sued Donald Trump, his father, Fred, and their apartment company in 1973 — is less common than it was. (The Trumps settled out of court, promising not to discriminate without admitting wrongdoing.) Yet successive presidential administrations have balked at full enforcement of the 1968 law’s requirement that federally aided local governments take “affirmative” steps for residential desegregation. Many predominantly white communities resisted; they were happy to take federal money but didn’t want fair-housing strings attached.

The Obama administration wrote regulations to carry out this long-dormant provision in 2015, but President Trump’s housing secretary, Ben Carson, who previously denounced the whole idea as “social engineering,” recently postponed implementation of the Obama rule until late 2020.

Ironically, the purpose of these federal regulations in many cases would be to counteract the effect of other government rules, enacted at the local level: Land-use restrictions — zoning, minimum lot sizes, growth controls and the like — that effectively enable upper-income households to create their own residential enclaves are a major culprit in the persistence of segregation by both class and race.

Deregulating local residential real estate might get at the root causes more efficiently. A recent paper by Michael C. Lens and Paavo Monkkonen of the UCLA Luskin School of Public Affairs suggests that state government intervention can help, by offsetting local interest group pressure.

As social “sorting” and political polarization advance, it seems more important than ever to tear down barriers that prevent Americans from living together as equals.

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