On Friday, the Department of Homeland Security announced that it was expanding its 287(g) program, which enlists local law-enforcement agencies to hunt illegal immigrants, with 11 new partnerships across the country. The department also announced steps to improve oversight of 287(g), which has been plagued by reports of racial profiling and abuse — particularly in Arizona, home state of the Homeland Security secretary, Janet Napolitano. But Ms. Napolitano should be deep-sixing this program, not tweaking or widening it.

Don’t just take our word: many responsible police chiefs and sheriffs have stoutly opposed having immigration duties outsourced to them. The Police Foundation, a nonprofit research group, declared in a study in April that the costs of 287(g) outweigh the benefits, not just because it strains budgets, but also because it undermines community policing, which relies heavily on building trust among those the officers serve and protect.

Turning local cops into immigration enforcers makes racial profiling more likely while sending a chill through immigrant neighborhoods, where victims fear and avoid the police and crimes go unsolved for lack of witnesses. As a police chief in the report said: “How can you police a community that will not talk to you?”

If that weren’t bad enough, the administration also announced last week that it would continue the Bush-era practice of requiring federal contractors and subcontractors to use E-Verify, a deeply flawed electronic system for checking people’s eligibility to work. Since its databases are full of mistakes, this all but guarantees that citizens and legal residents will lose their jobs.

The federal government created huge problems by letting the immigration system founder and fester, and President Obama inherited a bad enforcement system. But the mess is not going to be cleaned up by making more local immigration posses or by unjustly firing tens of thousands of innocent citizens and legal residents just to get at undocumented immigrants.

Enforcement-only schemes were the rage back when anti-immigrant demagogues were in full roar and Bush officials wanted to show how tough they were. They bring us no closer to an immigration system that works. Mr. Obama promised fresh ideas on immigration reform. So far we don’t see them.