I have a new column in today's Boston Globe about the shrinking number of counties that are competitive in presidential elections. The map above highlights counties where the winning margin was less than 10 points in 1976 and in 2004. An excerpt:
More than 36 million voters, or 30 percent of the electorate, lived in counties where President Bush lost to John F. Kerry, and lost big by at least 10 percentage points. (This compares with only 25 percent who lived in counties where Nixon beat John F. Kennedy by such a margin in 1960, though Nixon came closer to winning.) These voters were concentrated in New York, Boston, and most of the nation's biggest cities. And though Bush won the election by less than 3 percentage points, almost 50 million voters, or 41 percent of the electorate, lived in counties that he carried by double digits. These included exurban counties around such Sun Belt cities as Atlanta.
Though the contest between Bush and Kerry was tight at the macro level, only 29 percent of voters lived in counties where the victory margin was less than 10 points — where the winner wasn't evident within an hour of the polls closing. That's lower than the 32 percent who lived in competitive counties in 2000; the comparable figures were 46 percent in the Carter vs. Ford race of 1976 and 34 percent in the Kennedy vs. Nixon race.
UPDATE: Partly because Obama won nationwide by a solid 7-point margin, there were even fewer competitive areas in 2008, with only 26 percent of voters (34 million out of 131 million casting ballots) living in counties where the victory margin was less than 10 points. The 721 closely fought counties are in the lightest shades on this New York Times map.
For a list of the biggest shifts away from the GOP, see "Where were Obama's biggest gains for the Democrats in 2008?"
The largest county to fall out of the competitive list was San Diego, California, which went from a 6-point win for Bush in 2004 to just over a 10-point win for Obama. Miami-Dade, Florida, went from a 6-point win for Kerry to a 16-point win for Obama; and Dallas County in Texas went from a 1-point edge for Bush to a 15-point win for Obama. On the other side of the political spectrum, Garland, Arkansas (which includes Hot Springs), went from a 9-point win for Bush to a 25-point win for McCain.
Harris, Texas, was the biggest county to become competitive, going from a 12-point Bush win to a 2-point Obama win. And California's Orange County went from a 21-point victory for Bush to a mere 3-point win for McCain. It is quite possible that these counties will continue to trend Democratic in 2012 even if the Republicans win enough smaller counties elsewhere to take back the White House.