The National Guard's arrival may bring order to Ferguson, Mo. It probably won't bring peace. It didn't in Newark and Detroit after race riots in 1967, nor in Los Angeles after the Rodney King verdict in 1992. However necessary, sending in the guard -- as Missouri Gov. Jay Nixon did for Ferguson early Monday -- is usually an admission of failure that becomes as much a part of a community's stigma as the rioting it's designed to stop.