President Obama touts job retraining at community colleges to enable laid-off workers to close the “skills gap.” Mitt Romney agrees that retraining is the answer. But it hasn’t worked in Janesville, Wisconsin, where a GM plant closed four years ago. Laid-off workers who took vocational classes at a nearby technical college ended up working less and earning less than their former co-workers who didn’t go back to school. Why? There aren’t many jobs.