ONE OF THE MOST enduring, puzzling, and contentious phenomena of modern American political life is the persistence of firm Democratic Party majorities in Congress even as the Republicans tighten their stranglehold on the White House. The enduring nature of the phenomenon can easily be seen with a few simple numbers. The Democrats have controlled the House of Representatives for thirty-six consecutive years, and fifty-six of the last sixty; they have run the Senate for fifty of the past sixty years. The Republican Party, meanwhile, emerging in 1952 from the desert of two decades outside the White House, has successfully held the presidency seven of the past ten terms, including three in a row and five of the past six. Since 1954, the United States has had eighteen years with a Republican president and a Democratic Congress, six years with a Republican president and Senate and a Democratic House, and only twelve years with a president and Congress of the same party.