Last January, as his presidential campaign was stirring to life, Howard Dean was asked why he had decided to keep nearly half of his records as governor of Vermont under seal until 2013. "Well, there are future political considerations," Dr. Dean told statehouse reporters. "We didn't want anything embarrassing appearing in the papers at a critical time in any future endeavor." Dr. Dean now says he was joking about why he invoked executive privilege to keep 145 boxes of his official records — about 47 percent of them — under a 10-year seal. But there is ample evidence in the...