In announcing his wrongheaded proposal to increase the minimum wage to $9 an hour, President Obama spoke in lofty terms: “In the wealthiest nation on earth,” he said in his State of the Union address last month, “no one who works full time should have to live in poverty.”If the debate proceeds as it has — many times — in the past, then most Democrats will embrace the president’s message and back the proposal, while most Republicans will oppose it, on the grounds that higher labor costs will lead to higher unemployment.But we shouldn’t rely on political opinions in this debate. Facts clearly demonstrate that raising the minimum wage is a bad idea.The case against raising the minimum wage is straightforward: A higher wage makes it more expensive for firms to hire workers. How big an effect does this have on the job market?