First in Detroit, then in Stockton, Calif., and now in New Jersey, judges and other top officials are challenging the widespread belief that public pensions are untouchable. Gov. Chris Christie of New Jersey delivered the latest blow on Tuesday, when he proposed to freeze that state’s public pension plans and move workers into new ones intended not to overwhelm future budgets or impose open-ended demands on taxpayers. The first crack came in Detroit, where a judge ruled that public pensions could, in fact, be reduced, at least in bankruptcy. Then, just a few weeks ago, an opinion by the bankruptcy...