Rob Davis, police chief of San Jose, Calif., and president of the Major City Chiefs Association whose members include police chiefs of the 57 largest U.S. cities, said the law will undermine that compact. "We're the ones actually doing the police work in some of the most diverse communities in the country ... and we're concerned it's going to drive a wedge between our efforts to try and establish these community policing relationships that we worked so hard to develop over the last several years."

John Harris, head of the Arizona Association of Chiefs of Police and Police Chief in Sahuarita, Ariz., said the law will put police in an untenable position of being accused by opponents of the law of racially profiling immigrants and by supporters of the law of  not doing their jobs. It puts Arizona law enforcement right in the middle of these two sides and that's not where we want to be, particularly for something we think is a federal responsibility and not a local responsibility," he said.

For a moment I wondered if I was witnessing some cracks in the Blue Wall of Silence. OK, that's probably an overstatement; the chief's aren't exactly refusing to close ranks around an errant cop. Still, by publicly challenging a law they find troubling and difficult to enforce, they are closing ranks around an important principle. That counts for something.

The chiefs have not gone unnoticed by the civil rights community. Both the NAACP and MALDEF cited opposition to the Arizona law by "several prominent law enforcement groups" in statements the organizations put out when they joined a broad coalition of civil rights groups that filed a federal class-action lawsuit challenging the law.

"I think it is a helpful moment and illustrative on a number of levels," said Hilary O. Shelton, director of NAACP's Washington bureau and senior vice president for advocacy and policy. "This may be just the thing to crack open the door for us to have more discussions around other issues of concern, beyond racial profiling, to areas such as use of force and other challenges between police officers and local communities."

The law was clearly designed to target the nearly 500,000 undocumented immigrants in Arizona, the majority from neighboring Mexico. Arizona Gov. Jan Brewer, who is scheduled to meet with President Obama today to discuss the law and illegal immigration in her state, has insisted that the law expressly prohibits racial profiling. She says that only those stopped by police for other reasons such as a traffic violation, a busted headlight, or a host of other minor civil infractions would be questioned about their immigration status. But she has yet to convincingly articulate how police will accurately determine whom to question and arrest based on a "reasonable suspicion," and how they will avoid arresting legal American citizens of Hispanic descent who were either born here or are naturalized citizens.

If the governor who signed the law into being can't guarantee it will protect the rights of state residents, why should police be expected to enforce it? Maybe Arizona's various police chiefs should take a page from the other opponents of the law who have organized marches, sit-ins and other civil disobedience actions to protest the law; maybe they should simply refuse to enforce it. Now that might make for a lasting friendship with civil rights groups.

Marjorie Valbrun is a senior writer at America's Voice, an organization that advocates for reform of the immigration system.

Like The Root on Facebook. Follow us on Twitter.