His megadonors are from Chicago. His brain trust is from Wisconsin. And Iowa is the campaign linchpin. When he formally announces his presidential bid in a Milwaukee suburb next week, Scott Walker’s campaign will have an unmistakably Midwestern stamp on it, from a stump speech that features giant Midwestern retailer Kohl’s to a primary season strategy pegged to Iowa and Michigan. The idea is to position the Wisconsin governor as the favorite son of the Midwest, where he hopes to run up the score beginning with Iowa next February. Walker has so far raised nearly $30 million for his effort,...