So far in the campaign, Barack Obama has generally refrained from going after the most critical weakness of Hillary Clinton's candidacy: the fact that the Clinton whom Democrats really like is Bill, while Hillary, who now presents herself as the voice of experience, got most of that experience as First Lady, first of Arkansas, then of the United States. Until now, no one has ever suggested that being married to a former President constituted a qualification for the office. Today, Obama took the gloves off. He attacked Hillary's support for NAFTA, and Hillary responded by trying to distance herself from...