New York City’s immigration sanctuary laws are under attack. President Trump, and more recently Mayor Adams, claim that the city’s refusal to participate in federal deportations undermines public safety. Lost in the public debate, however, is the reality of how these laws were specifically crafted to help the NYPD fight crime. Fourteen years after their initial passage, the record is clear: contrary to the rhetoric, New York’s sanctuary laws have proven to be potent crime fighting tools. Thankfully, neither Trump nor Adams has the power to roll back the city’s sanctuary laws. Only the City Council can do that. That is why it is so important that the Council stand firm in its resolve to protect public safety and resist calls to repeal or weaken New York’s sanctuary laws. Understanding the history and origin of these laws is critical to that effort. In 2009, Make the Road New York, the state’s largest membership-based immigrant advocacy organization, approached me and my clinic students at the Cardozo School of Law with a problem: its members were afraid of the police. When people from communities of color called the police, they never knew who was going to end up in handcuffs — too often it was their children, their spouses, or their parents, and they just couldn’t take that risk. NYPD arrests had become a gateway to the deportation pipeline, with thousands of people each year being funneled into immigration detention. Immigrant families were being torn apart, and fear of police was growing. As a result, immigrant witnesses and victims of crime were increasingly unwilling to work with the NYPD. My students and I set out to change that. The legal mechanism that triggers transfers from local police to federal immigration detention is called an immigration “detainer.” They are nothing more than pieces of paper signed by a line-level immigration officer. However, at that time New York City, like every other state and locality across the country, believed those papers were legally binding commands to hold people for deportation. Two of my students uncovered a solution — they had learned about a constitutional doctrine protecting states from being forced to execute federal programs. If local sheriffs couldn’t be forced to do federal background checks for gun purchasers, as a seminal Supreme Court case held, local police and jails should not be forced to hold people on federal immigration detainers. My students’ shockingly simple solution had eluded legal thinkers. Their argument would eventually be adopted by the New York City Law Department, the federal courts, and even by federal immigration authorities themselves, becoming the foundation for hundreds of sanctuary laws nationwide. With the legal barrier cleared, support grew quickly for a first-of-its-kind law to limit which people the city would hold for federal immigration authorities. While many have powerfully argued that no one should be subjected to the broken and brutal deportation system, that is not the approach the City Council took. It chose to limit, not end, cooperation with federal authorities — agreeing to honor detainers for people who have been convicted of violent or serious crimes. The immigrant community and their advocates were unsurprising enthusiasts — but these laws also gained robust backing from law enforcement leaders like the legendary Manhattan District Attorney Robert Morgenthau and the Major Cities Chiefs Association. They understood that entangling local police and federal immigration authorities resulted in increased crime. The Council’s leadership sparked a wave of similar laws across the country, and, over time, these laws have delivered the public safety benefits anticipated by law enforcement leaders. NYPD data shows nearly 90,000 fewer major felonies committed in the city in the decade following the passage of the first sanctuary law than in the preceding decade. While a variety of factors impact crime rates, comprehensive studies make it clear: cities with sanctuary laws have lower overall crime rates. The last time Trump took aim at these laws, New York had unflinching leaders willing to stand up for immigrant New Yorkers and for public safety. This time, unfortunately, Adams has demonstrated an increasing hostility toward immigrant New Yorkers and a suspicious interest in currying favor with the incoming president. Thankfully, the City Council, not our weak-kneed mayor, has the last say. The Council must stand firmly behind our laws that provide sanctuary, not just for immigrants, but for the safety of all New Yorkers. Markowitz is a professor at Cardozo School of Law and co-director of the Kathryn O. Greenberg Immigration Justice Clinic.