An article this morning in the Des Moines Register may give Sanders supporters cause for concern. As Anne Selzer points out, twenty-seven percent of his Iowa supporters are concentrated in just three counties: Black Hawk (home of the University of Northern Iowa), Johnson (home of the University of Iowa), and Story (home of Iowa State). Together these three counties account for about 10% of all Iowa caucuses (162/1682).
While Sanders will undoubtedly dominate these Caucasus, this concentration of support does him no favors in the final delegate count. And it is possible that the news for Sanders is even worse. If (as seems likely) his supporters are particularly concentrated in the three University towns (Cedar Falls, Iowa City, and Ames), that means that he has a commanding lead … but in just 60 caucuses (<4% of the total).