The Baltimore County executive, C. A. Dutch Ruppersberger, knew the national Democratic Party was eager — or to put it bluntly, desperate — for him to win the open House seat here in Maryland's Second District. Even so, he was a bit surprised by what the party bestowed on him. First, he started getting advice from Representative Elijah E. Cummings, who has represented parts of the urban core of Baltimore since 1996. Mr. Cummings told him to start running far more commercials on black radio stations and to have black political leaders record messages that can be automatically telephoned to...