Obama's Line in the Sand on Immigration Enforcement

The Goldwater study found that since Arpaio's immigration sweeps began, violent crime rates in Maricopa County have jumped by over 69 percent—including a 166 percent increase in homicides in the past three years—while the sheriff's department's clearance rate has fallen to just over 50 percent. While Arpaio has been pouring resources into his immigration sweeps, which the Goldwater group concludes "are ineffective in policing illegal immigration and in reducing crime generally," much-needed resources have been diverted away from basic law-enforcement.

Arpaio himself has said his department is "quickly becoming a full-fledged anti-illegal-immigration agency," but as of December, its eight sweeps, which have involved hundreds of deputies and thousands of work days, had netted only a few hundred illegal immigrants. According to the Goldwater Institute, city police departments in the Phoenix suburbs that rely on standard police procedure—investigating violent crimes and determining the immigration status of suspects after they are booked—arrest many more dangerous illegal immigrants. Arpaio's own department has identified 16,000 illegal immigrants this way in recent years, far more than it has picked up in its sweeps.

"There are very serious criminal law enforcement issues that are raised when you have local police involved in immigration enforcement," says Johnson, the dean of the UC-Davis School of Law. "There is a lot of potential for abuse. Things like the tent prisons and pink underwear and 'America's toughest sheriff' kind of talk—that's kind of a red flag." Johnson, for one, sees the investigation of Arpaio as a way for the Obama administration to draw a line in the sand: "At the minimum, this is a signal that this administration's going to try to make sure all immigration enforcement is professionally done."

The Justice Department investigation of Arpaio is expected to take several months.