Curious how many Democrats live on your block? Just download the Obama campaign's new mobile app. The app, released last week, includes a Google map for canvassers that recognizes your current location and marks nearby Democratic households with small blue flags. For each targeted address, the app displays the first name, age and gender of the voter or voters who live there: "Lori C., 58 F, Democrat." All this is public information, which campaigns have long given to volunteers. But you no longer have to schedule a visit to a field office and wait for a staffer to hand you...