A mysterious $250,000 donation used to bankroll a political committee controlled by a potential candidate for the Democratic presidential nomination in 2008, John Edwards, highlights a gap in federal laws requiring reporting of political contributions. In June, a closely held company gave a quarter of a million dollars to the One America Committee, a so-called 527 organization affiliated with Mr. Edwards, who became the Democrats' vice presidential nominee in 2004 after making a spirited but ultimately unsuccessful bid for the presidential nomination. A report that the committee filed with the Internal Revenue Service identified the donor as Oak Spring Farms,...