Over the past two presidential races, the electoral map has been remarkably stable. It's well known that from the 2000 to the 2004 elections, only three states switched hands -- with George W. Bush taking New Mexico and Iowa in 2004 after losing them to Al Gore in 2000, and John Kerry swiping New Hampshire from Bush after the president carried it in 2000.
This rigidity is reinforced at the micro level. Of the 3,107 counties in the lower 48 states, only about 7 percent switched hands between 2000 and 2004, with Bush winning 156 counties that he had lost in 2000, and losing 67 that he had won, according to figures provided by Polidata, a political data-analysis firm. About three-fourths of the nation's counties voted for Bush both times; another one-sixth, many of them larger counties along the East and West coasts, backed both Gore and Kerry. The persistence of this partisan divide underscores the challenges facing Barack Obama and John McCain as they try to expand their reach into areas often conceded to the other party.
One key reason so few counties changed hands in the past two elections is that so many now lean decisively to one party or the other. At the national level, Bush beat Kerry in 2004 by about the same margin (2.4 percentage points) as Jimmy Carter beat Gerald Ford in 1976 (2.1 percentage points). But over that period, the number of "landslide" counties -- carried by one party or the other by at least 20 percentage points -- exploded: from 37 percent of the nation's counties in 1976 to 60 percent in 2004.
Put another way, in 1976, only one-quarter of American voters lived in counties decided by landslide margins. By 2004, that figure had nearly doubled to 47 percent.
This article appears in the August 30, 2008 edition of National Journal Magazine Contents.