Unions are under attack in the United States — not only from people like Gov. Scott Walker of Wisconsin, but now, with the teachers strike in Chicago, from the very core of President Barack Obama’s inner circle, his former chief of staff and current mayor of that city, Rahm Emanuel. Twenty-five thousand teachers and support staff are on strike there, shutting down the public school system in the nation’s third-largest school district. This fight now raging in Chicago, Obama’s hometown, has its roots in this historic stronghold of organized labor and in the movement started one year ago this week, …