Republicans only need one of the two seats to maintain their Senate majority. A look at the history of similar contests indicates that an electoral split is uncommon, but still possible.The presidential race seems to be over. Republicans gained seats in the House, but Democratic control is assured there too, if narrowly. Only the Senate stands between the Democrats and undivided government, with the majority there to be decided by two runoff elections in Georgia. As close as that state was in the presidential race—a margin of 0.25 percent, according to the hand recount just finished—we can expect the Senate...