On Monday, the nation honored the towering legacy of the Rev. Dr. Martin Luther King Jr. But the progress he demanded remains unfinished, and nowhere more than in the deeply segregated neighborhoods many of us call home. Dr. King understood that where a person lives determines so many of their opportunities, including access to good jobs, schools, health care, food and safety. Barely a week after Dr. King’s assassination, Congress passed the Fair Housing Act with overwhelming bipartisan support in recognition of this truth.

In the more than 50 years since its passage, the Fair Housing Act has helped fight discrimination in mortgage lending, zoning restrictions that prevent people from being able to choose where to live, and local landlord abuses. In 1973, the United States government used it to charge Fred Trump and his son, our current president, with housing discrimination. Rather than fight those charges, the Trumps signed a consent decree requiring changes to the way they managed their properties. The Fair Housing Act was the only backstop for the people the Trump family discriminated against, and now the Trump administration is seeking to gut its protections.

Key to those protections are two principles established by Congress and enforced by the Department of Housing and Urban Development (HUD), where I was secretary under President Barack Obama. The first is “disparate impact,” which makes clear that policies or practices that discriminate against people of color or other protected groups are illegal even without proof they are intentional. For example, if white couples are regularly approved for mortgages but black couples with the same qualifications are rejected, the bank must fix their loan process, even if its employees didn’t have racist intentions. Under disparate impact, it’s the results that matter.

The second is a mandate that communities “affirmatively further fair housing,” which requires government to promote greater opportunity and integration as well as fight discrimination. For example, if a city’s affordable housing is all located in black neighborhoods with failing schools, limited transportation, and poor health care, that city must make an effort to fix the problems in those neighborhoods and build new affordable housing in other neighborhoods, in addition to ensuring there’s no racial discrimination when any of the individual apartments are rented out.