THE NEW FAD in American politics in 2004 was data mining. The Republican and Democratic National Committees invested heavily in building large databases that used consumer marketing information to segment voters into groups for highly customized communications.

JOHN KERRY is betting much of his presidential campaign on voter anger over lost American manufacturing jobs in the industrial Midwest. Seldom does a day go by without a Kerry attack on lost jobs in battleground states such as Michigan, Ohio, and Missouri, often wrapped up in hot rhetoric about…