This bill, known as the "Shut Down Sanctuary Policies Act," seeks to improve public safety by significantly strengthening the enforcement of federal immigration laws across the United States. It amends the Immigration and Nationality Act to ensure that state and local government entities are not prohibited from cooperating with or enforcing federal immigration laws. The legislation explicitly supersedes any state or local laws, ordinances, regulations, or policies that restrict such cooperation.

The bill outlines specific law enforcement activities that state and local personnel must be allowed to undertake, including making inquiries about immigration status, maintaining related information, and notifying federal authorities about encountered individuals. To encourage compliance, it grants state and local entities immunity from liability for actions taken in accordance with these provisions, treating them as acting under federal authority. Such entities would also be able to remove related civil actions or criminal prosecutions to federal court, with the U.S. Government substituted as the defendant, except in cases of mistreatment.

Furthermore, the legislation clarifies and strengthens the authority of Department of Homeland Security (DHS) detainers. It mandates the Secretary of Homeland Security to issue detainers for individuals arrested for criminal or motor vehicle offenses if there is probable cause to believe they are inadmissible or deportable aliens. Probable cause can be established through various criteria, including biometric confirmation, ongoing removal proceedings, prior removal orders, or reliable evidence of inadmissibility.

A critical provision of the bill introduces severe consequences for non-compliant jurisdictions. States and local governments that restrict cooperation or fail to honor valid DHS detainers will lose eligibility for various federal grant programs, including those administered by the Department of Justice and DHS related to law enforcement or immigration. The Secretary of Homeland Security is also granted discretion to decline transferring custody of aliens to non-compliant jurisdictions and is prohibited from transferring aliens with final removal orders to them. Additionally, the bill establishes a private right of action, allowing victims of certain violent crimes committed by aliens to sue state or local governments if the alien was released from custody due to the jurisdiction's failure to honor a detainer or its "sanctuary" policies.