DES MOINES | Ted Cruz has assembled an impressive presidential campaign structure in Iowa, veteran political observers here say, with one going so far as to describe Cruz's campaign as perhaps "the most sophisticated" the first-in-the-nation caucus state has ever witnessed.Because of that grassroots organization, Cruz is primed to maintain his recent surge in the polls and win the Iowa Republican caucuses in five weeks, those observers say.Cruz, a tea party firebrand and first-term U.S. senator from Texas, was the first Republican candidate to enter the presidential race, on March 23. Nine months later, he has overtaken longtime front-runner Donald...