After more than two decades as a fixture of federal politics, Amy Klobuchar has turned her gaze homeward, announcing a bid for the Minnesota governorship at a moment when her own party's stewardship of the state has left voters restless. Her candidacy is a wager that proximity to power in Washington can be recast as distance from the failures closer to home — that a senator can become a reformer simply by changing the stage. The deeper question her campaign raises is an ancient one in democratic life: whether a leader known for bridging divides can also summon the will to break them.