The road changes just past the Starr County sign. The shoulder disappears, the grass is left uncut and the black-eyed Susans and big pink Texas sage have to compete with the orange traffic cones set out by the border patrol. Just two counties up from the Texas tip, where the flood plains along the Rio Grande change to rolling hills and eroding cliffs, Starr County, largely Mexican-American, is one of the poorest counties in the nation. Fifty-nine percent of its children live below the poverty level, and in the strange new arithmetic of want, in which poverty means not starvation...