How do sanctuary cities affect ICE's ability to detain undocumented immigrants with criminal records?
Executive summary
Sanctuary policies limit or condition local cooperation with federal immigration enforcement—most often by refusing ICE detainer requests, limiting information-sharing, or barring local arrests for civil immigration violations—which can reduce the number of people ICE can pick up directly from local jails but do not create a blanket shield against federal detention [1] [2] [3]. Empirical research finds sanctuary policies reduced some deportations without increasing violent-crime removals, while ICE and critics argue those policies hamper federal access to suspects already in local custody [4] [5] [6].
1. What “sanctuary” actually means in practice
“Sanctuary” is not a single statute but a patchwork of local rules that typically restrict honoring ICE “detainer” requests, limit asking about immigration status, or deny ICE access to jails; some jurisdictions nevertheless rent jail space to the federal government or permit limited notification arrangements, so practices vary widely [1] [5] [7]. Courts and federal guidance have long treated ICE detainers as requests rather than mandatory commands, and several circuits have held localities are not legally required to hold people for ICE beyond brief periods absent a warrant [2].
2. Measured effects on ICE’s ability to detain people with criminal records
Rigorous studies combining ICE removal records and FBI arrest data conclude sanctuary policies implemented 2010–2015 reduced certain deportations but did not materially lower the removals of people with violent convictions or increase local crime rates, suggesting the effect on ICE’s ability to detain the most serious offenders is limited [4] [5]. Other academic work argues sanctuary practices can reduce the entanglement of local policing with immigration enforcement and may even correlate with stable or lower crime rates, complicating claims that such policies directly impede removal of dangerous individuals [8].
3. How ICE compensates operationally
ICE often prefers to apprehend people already held in local jails because it is faster and safer, and when local cooperation is reduced, ICE resorts to other pathways: its own field arrests, increased use of federal-state deputization programs like 287(g), expanded data-mining (Secure Communities-type linkages), or incentives to recruit local partners—tactics that blunt but do not erase the impact of sanctuary limits [9] [10] [11]. Federal administrations can also pursue executive actions, new statutes, or funding cuts to pressure jurisdictions, and some states have passed laws forcing cooperation or banning sanctuary measures; these political levers alter how effective sanctuary protections are on the ground [7] [12] [9].
4. The public-safety and legal argument duel
ICE and critics assert that refusing detainers releases potentially dangerous people back into communities and undermines public safety, a claim emphasized by political messaging and some advocacy groups that label sanctuary jurisdictions as “shielding criminals” [6] [12]. Local leaders, civil-rights advocates, and several empirical studies counter that sanctuary policies protect public safety by preserving community trust with police, reducing underreporting, and not increasing removals of violent offenders; they also highlight constitutional and civil-rights risks when local officers act as immigration agents [3] [1] [8] [4].
5. Hidden incentives and political agendas shaping the narrative
Maps and lists produced by partisan groups frame sanctuary practices either as obstruction (Center for Immigration Studies) or as necessary civil-rights protections (ILRC, Global Refuge), reflecting advocacy-driven framing that colors public debate and policymaking [6] [7] [1]. Federal administrations seeking tougher immigration enforcement have incentives to portray sanctuary policies as operational choke points to justify funding shifts, legal threats, or expanded deputization programs, while local officials have incentives to emphasize public-safety benefits to preserve community trust and voter support [9] [13].
6. Bottom line
Sanctuary policies can and do reduce ICE’s straightforward ability to take custody of undocumented people from local jails by limiting detainer compliance and data-sharing, which lowers some deportations, but they do not insulate all people with criminal records from federal action; ICE retains alternative tools—federal arrests, 287(g), intergovernmental contracts, and policy levers—that mitigate the effect, and the strongest empirical studies find sanctuary implementation did not reduce removals of violent offenders nor increase local violent crime [4] [11] [5] [10]. The real-world outcome depends on the exact local policy, state preemption or cooperation laws, federal priorities, and political maneuvers—meaning sanctuary cities shape but do not determine ICE’s capacity to detain undocumented immigrants with criminal records [7] [9] [2] [3].