A federal judge in Boston ruled in late May that the Trump administration cannot force local law enforcement to help facilitate ICE arrests. It’s the latest in a string of defeats for the federal government, which has been seeking to invalidate “sanctuary city” policies around the country.
The government argues that ICE officers cannot adequately protect the public unless police and prosecutors work in lockstep with their aggressive enforcement agenda. But in a friend-of-the-court brief filed by the Brennan Center, former law enforcement officials argued that enlisting local police, prosecutors, and corrections officials in President Trump’s aggressive immigration enforcement tactics could compromise public safety by diverting finite city resources and degrading immigrant communities’ trust in law enforcement. The court’s decision underscores that cities are within their constitutional rights to choose not to run those risks.
Sanctuary Cities and the Boston Litigation
Starting in the 1980s, cities across the country began adopting laws and policies that limited the use of state and local resources for federal civil immigration enforcement. These “sanctuary city” policies may, for example, direct local jails not to honor an ICE “detainer” — a request to hold someone in custody past their release date to facilitate a handoff to ICE. Other policies may limit the types of information that police will share with ICE.
Trump’s aggressive immigration agenda puts these policies back into the national spotlight. Immigration arrests surged from around 400 per day before the inauguration to more than 1,000 per day in late 2025. Historically, ICE prioritized arrests of people with criminal convictions. But the agency is increasingly arresting people with no criminal conviction history. Similarly, the number of people detained by ICE grew from around 40,000 to more than 60,000. The administration has also waged an unrelenting legal battle to force jurisdictions to repeal their sanctuary policies or otherwise invalidate them to facilitate more aggressive immigration enforcement in those cities.
The Boston case is one of more than a dozen lawsuits filed against cities around the country, seeking to overturn sanctuary policies as contrary to the Constitution’s Supremacy Clause. That provision protects the federal government’s right to set national policy on some subjects. Cities, in response, have pointed to the 10th Amendment, which reserves other policy areas to state and local governments — including, traditionally, law enforcement.
At issue in this case was the Boston Trust Act, enacted by the Boston City Council in 2014. Among other things, the law specifically forbids local officials from honoring ICE detainer requests or sharing information with immigration officials unless required by federal law. In passing the measure, city policymakers emphasized the public safety benefits of encouraging positive, collaborative relationships between immigrant communities and law enforcement.
In the litigation, the Justice Department argued that Boston’s sanctuary policies — especially those regarding detainer requests and information-sharing — amounted to “an untrammeled right to forbid all voluntary cooperation by state or local officials with particular federal programs,” infringing on the federal government’s constitutionally protected interest in the orderly enforcement of immigration law. The federal government also claimed that it would be unable to apprehend immigrants who have committed serious crimes without being able to enlist local police.
The district court disagreed. The court didn’t reach the merits, instead finding that the federal government lacked standing — a legal doctrine that requires plaintiffs to identify a particular injury, traceable to the defendant’s acts, and redressable by a favorable decision. Neither of the government’s core concerns with the Boston Trust Act cleared that bar. First and foremost, Massachusetts state law separately forbids law enforcement from detaining someone “based on a federal civil immigration detainer or administrative warrant.” Thus, even if the federal government prevailed, Boston officials would be obligated by other laws to continue refusing ICE detainer requests. Second, the court concluded that the Boston Trust Act forbade sharing “personal information” about people it interacted with, but that the statute explicitly “does not prohibit” agencies from sharing information on immigration status, as required by federal law.
The court also expressed some frustration with how the case had been litigated. The government could have revised its case to address some of these defects but seemed to express no interest in doing so. In addition, four similar lawsuits had already been dismissed in courts around the country, but the government “largely ignored those thoughtful, persuasive opinions and did not attempt to explain why this Court should reach a different conclusion,” the court wrote. The court further characterized as both “sweeping” and baseless the government’s unusual theory that Boston’s perceived defiance of the administration’s political priorities had somehow itself conferred legal standing.
Law Enforcement Perspectives on Sanctuary Cities
The Brennan Center and several other groups filed friend-of-the-court briefs on the motion to dismiss that were acknowledged by the court in a footnote. Brennan’s brief offers the perspectives of a group of former law enforcement officials. Based on their experience, the former officials observed that sanctuary policies can enhance public safety and that the 10th Amendment empowers local leaders to make that policy judgment.
In their brief, the group noted that mingling immigration and criminal law enforcement risks involving officials in federal immigration “responsibilities that fall outside their training,” “divert[ing] them from other public safety priorities,” and sowing distrust within immigrant communities. These arguments go to the core of the constitutional issues in these cases, reinforcing why cities and states, not the federal government, should be setting local law enforcement priorities for their own communities.
Police and prosecutors face unique challenges when seeking to build trust with immigrant communities. Around 70 percent of undocumented immigrants report that they are less likely to contact the police if they are a victim of a crime, fearing that police officers will use the interaction as an opportunity to inquire into their immigration status. Law enforcement policy guidance notes that even those with legal status may avoid reporting crimes due to concerns that they will be racially profiled and wrongly presumed to be undocumented.
Sanctuary laws help build trust by clarifying that police and prosecutors seek to protect the safety of all residents. Empirical research cited in the brief supports this theory. At a descriptive level, counties with sanctuary policies have statistically lower rates of crime and stronger economies than comparable counties without them. By contrast, research shows that legislation requiring state and federal cooperation on immigration enforcement results in a decrease in 911 reporting calls, a strong indicator of declining community trust.
The brief was filed before aggressive immigration enforcement in Minneapolis made national headlines. But Minneapolis’s experience starkly illustrates the risks it sought to convey. Minneapolis law enforcement officials repeatedly warned that large-scale ICE deployments interfered with their work and made the city less safe. (At one point, ICE outnumbered local police by a three-to-one ratio.) Law enforcement leaders described instances of racial profiling and unlawful stops of residents, as well as direct interference with officers in their responsibilities. As Hennepin County Sheriff Dawanna Witt argued, “Trust is an essential element of public safety.” Yet, she continued, that trust was “being damaged, broken, by the questionable and sometimes unethical actions” of some federal agents.
