Janet Napolitano's embarrassing history with Sheriff Joe Arpaio.

Of course, few governors arrive at their offices without having made a few malodorous alliances. And Arizona is one of the most conservative states in the nation, where a tough stance on immigration is necessary even to get elected dog catcher. Still, when presented the opportunity to challenge a law-enforcement practice that was splashy and crowd-pleasing but ultimately cruel and futile, Napolitano declined.

Her history with Arpaio isn't necessarily a disqualifying factor. But it is something to consider. The secretary of the Department of Homeland Security cannot be reluctant to stand up and speak out against excesses in law enforcement.