...from the attached article, this is an example of what transpires in a Sanctuary City...
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What Does a Sanctuary City Policy Really Do?
In terms of immigration issues, sanctuary city policies are often designed to respond to a series of events involving undocumented individuals. The following is an example of such a series of events, and how the sanctuary policies apply.
Initial Contact with Law Enforcement: This is often something relatively common, such as an officer pulling over a car for speeding or responding to a domestic incident. This initial contact has nothing to do with citizenship status.
Law Enforcement Detains an Individual: Law enforcement books and takes fingerprints of the individual at the local or county jail. Per protocol, these fingerprints go through the FBI database. ICE regulations require that state and federal agents share information regarding inmates.
ICE Gets Involved: If ICE records show the individual is undocumented, ICE sends a request to the local jail to detain the individual for an additional 48 hours beyond the original release day and time. This time buffer allows ICE to seek a warrant and begin the deportation process.
Local Authorities React:According to the U.S. Department of Homeland Security, local officers do not have to comply with ICE requests for additional detention, because doing so is a violation of the Fourth Amendment.
The reaction of the local authorities depends on any sanctuary policies in place. Cities or counties with sanctuary policies typically decline the requests and release the individual once the appropriate time for the initial contact has been met. This might be because of charges dropped, bail set and met, or no jail time sentenced. Some sanctuary cities will reject all detain requests they receive from ICE, while others comply under certain circumstances including gang involvement, prior felony records, or terrorist watch list status.
Cities without sanctuary policies often comply with ICE and detain the individual while ICE seeks a warrant for deportation. The undocumented individual might remain in the local jail during the deportation process, or ICE might transfer that person to a federal prison. Jails and prisons that detain undocumented immigrants often receive federal funds for doing so.
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Note the symbiotic relationship between ICE and Private Prisons...i.e. the 'Jail First...ask questions later'. from the experience of Trump's "Zero Tolerance" program in his first term, it's a good chance this time it will be on steroids.
Link: https://www.globalrefuge.org/news/what-are-sanctuary-cities-and-why-do-they-exist-lirs/