In Alameda County, there’s rarely a new sheriff in town. Since 1986, there have been two sheriffs, and neither faced a challenger in any election. Some county residents, especially in the northwest cities of Berkeley and Oakland, want new leadership in the sheriff’s office. The current sheriff, Gregory Ahern, has been criticized for an array of problems with the county jail and is facing two class-action lawsuits brought by detainees, and a federal civil rights investigation. Critics also say his cooperation with federal immigration agents and an incident in which he sent an armored vehicle to evict activists who occupied a West Oakland home last year, show that his views are out of step with many voters.