Russo was painted into a corner in several ways. First, Oakland's enormous budget problems caused him to pair down the City Attorney's Office. Second, the election of Oakland Councilmember Jean Quan as Mayor of Oakland gave him a person more an adversary than an advocate to work with. Third, the counter-reaction to the Oakland Gang Injunction Program threatened to give Russo the first serious challenge to his office in the next election, should he have remained in Oakland.
Plus, John's in his 50s with two twin boys; he's not getting younger and it's time to be at a place where there's just less stress and bullshit. And frankly, Oakland City Hall was becoming more like a high school than a government office, with factions, cliques, games, groups, and enemies. Russo was tired of being part of that. He was concerned that his reputation would be sullied by that.
Now, thank God, he doesn't have to deal with it.
Oakland, or at least its current set of players, won't have Russo to kick around any more.
For a while.