WOODBRIDGE, Va. — The decision this week by John Thune, the Republican candidate for senator from South Dakota, to concede to his rival, Tim Johnson, the Democratic incumbent, virtually guarantees that Mr. Thune's narrow defeat will go down in conservative lore as the one lost to voter fraud on an Indian reservation. This charge probably won't ever be proved, but people on the right will continue to believe it — just as many people on the left think corruption in Florida cost Al Gore the presidency. In both cases, however, there's a better explanation for what happened. George W. Bush...