Democrats claim high voter turnout in their primaries is proof positive they'll win the White House in November. It is a familiar claim, made by one party or the other, that pops up every four years, but it contains not a morsel of truth. Many studies show no correlation between party primary participation and general election results. Nevertheless, in a memorandum to its supporters and the news media, the Democratic National Committee is crowing, "record turnout during the primaries has been transformational for the Democratic Party as record numbers of new voters are being registered." In this equation, new primary...