It's a working-class white concern, and a can't-miss issue for Obama. Richard Whitmire is president of the National Education Writers Association Barack Obama's advisers know that winning in Pennsylvania requires shrinking Hillary Clinton's wide lead among "Casey Democrats," working-class whites who were fond of their former Gov Robert Casey. The themes both Obama and Clinton aired out in Ohio to attract those voters, such as attacking NAFTA and decrying lapses in health-care coverage, undoubtedly will resurface in the coming weeks. But there's one more issue affecting these voters that the candidates haven't aired. And it's Hillary-proof. Anyone visiting the homes...