The 2012 presidential election can be seen as offering a choice between two visions of how to return us to this country’s golden age — from roughly 1945 to around 1973 — when working life was most secure for many Americans, particularly white, middle-class men. President Obama said his jobs plan was for people who believed “if you worked hard and played by the rules, you would be rewarded.” Mitt Romney explained his goal was to restore hope for “folks who grew up believing that if they played by the rules . . . they would have the chance to build a good life.” But these days, many workers have lost a near guarantee on a decent wage and benefits — and their careers are likely to have much more volatility (great years; bad years; confusing, mediocre years) than their parents’ ever did. So when did the rules change?