Michael Barone writes that recent elections have occurred within a very narrow range:
Some pollsters report an increasing percentage of voters identifying as independents. But fewer and fewer Americans vote that way. Straight-ticket voting, increasingly rare from the 1960s-1980s, has become more common today. In 2012, only 26 of the 435 House districts voted for a presidential candidate of one party and a House member of the other, the lowest number since 1920.
Presidential voting has become more predictable as well. Only three of the 50 states (Iowa, New Mexico and New Hampshire) voted for different parties' candidates in the 2000 and 2004 elections. Only two states (Indiana and North Carolina) voted for different parties' candidates in 2008 and 2012. You have to go back to the 1880s to find such partisan continuity.
A bigger swing in presidential voting occurred between 2004-08. But even then, only nine of the 50 states switched parties, and six of those had been carried only narrowly, with 50-52 percent of the vote, by George W. Bush. Of the other three, Indiana switched back to solidly Republican in 2012, North Carolina moved narrowly from Barack Obama to Mitt Romney and Virginia has, perhaps implausibly, become the national bellwether, with its percentages for the candidates matching national percentages more closely than any other state.
There is a big "however."
But what if the irresistible force scrambles the political map? This has always happened, sooner or later, in American politics. It has often been sparked by the rise of a disruptive candidate, running as an independent or as the nominee of a major party. Think Ross Perot, Ronald Reagan, George Wallace, Franklin Roosevelt, William Jennings Bryan, Abraham Lincoln. A disruptive candidate raises new issues, breaks across old party lines, brings new voters into the electorate.