+ What immigration policy reforms outside the amnesty fight should receive priority in the next administration?

David A. Martin is professor emeritus at the University of Virginia School of Law. He served as principal deputy general counsel of the Department of Homeland Security during the first two years of the Obama administration.

Donald Trump has made empowering local police to enforce federal immigration law a key part of his campaign. He has said that local agencies know where violators are and that they would be “so happy” to get them out.

But Trump apparently hasn’t been paying attention to what local jurisdictions have been doing over the past 10 years. A great many law enforcement agencies — including those covering large immigrant populations — have sharply restricted their cooperation with federal enforcement, even for violators arrested for local crimes and in the face of a formal federal request.

The reasons for this local stance reveal much about the counterproductive effects of “enforcement-first” policies. But they also indicate what must be done to achieve stable and sustainable immigration enforcement.

There are two strands to this local resistance: First, police leaders in immigrant-heavy areas are justifiably concerned that being closely linked to immigration enforcement will hamper community policing. They need good relations with the immigrant community to sustain communication and cooperation as they focus on their primary mission: public safety. This tension has always existed, but is now more pronounced because of the historically high percentage of unauthorized immigrants who have been living in the United States for a long time (60 percent of them have been here more than 10 years).

Second is the changing character of the public debate. The failure to enact a federal legalization program for long-term residents has generated many dramatically sympathetic cases of people facing removal. Anti-deportation activists have used these stories effectively to oppose virtually all deportations — a more extreme stance than localities had heard before.

Seen in this light, the hard-line enforcement camp’s success in blocking legalization, through 11 years of serious legislative proposals, has actually eroded public acceptance of immigration enforcement — evidenced by the resistance from many states and localities. Finally adopting legalization would counter-intuitively empower and legitimize enforcement by definitively assuring that federal officers focus on more recent arrivals. Effective enforcement against that group is the key to long-term deterrence of future violations, and also far more likely to rebuild sustained public support.

What would a broad legalization program mean for the future role of local law enforcement? Certainly not a return to the street sweeps that Trump envisions. They almost always ensnare both citizens and lawful immigrants. Experienced immigration officers, not local police, need to be the ones who both determine immigration status and apply consistent nationwide enforcement priorities.

Local police will always have an indispensable role, particularly in helping federal officers learn of immigration violators involved in crime. But they should concentrate on enforcing their own criminal laws, without regard to immigration considerations, under locally implemented (and federally monitored) safeguards against racial profiling.  Through database checks of all arrestees’ fingerprints, using a system that’s been in place since 2014, federal immigration officers will selectively request custody. After legalization, local cooperation should become routine.

Could this more focused connection to immigration enforcement still undercut community policing? That tension would still exist, but as many police executives recognize, it would be greatly reduced if Congress assured immigrants that the federal government will concentrate enforcement on recent violators.

If elected, Hillary Clinton will certainly press for early legalization. But to have a meaningful and enduring immigration legacy, she must also make resolute use of the full enforcement potential of such a move.

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