An Epochal Battle: The share of the public registered as neither Democrat nor Republican, but rather as independent, has exploded in recent years.

From The Wall Street Journal:

When Iowa voters walk into their state's caucuses tomorrow night, they will be kicking off a milestone campaign year that promises a new political course for America.

For the first time in 80 years, no incumbent president or vice president from either party is seeking the White House, creating an unusually unsettled campaign with no obvious front-runner. Power in Congress is divided so evenly between the two parties that neither has really been in control since the 2006 elections. Now, in the wide-open 2008 general election, voters will declare whom they want to run the executive and legislative branches.

Americans will make that choice at a time when they are distinctly uneasy. Record numbers of voters are choosing to declare themselves politically independent -- and thus open to moving either left or right. Both the Republican president and the Democratic Congress are receiving historically low public-approval ratings, another sign of voter unease.

Now the stage is set for an ideological rethinking in both parties. "The mood for change is more than one of small incremental adjustments," write Republican pollster Bill McInturff and Democrat Peter Hart, who conduct the Journal/NBC News poll. "It is concern for the next generation as well as widespread unhappiness with both President Bush and the Congress."

Elections that really turn the country in a new direction are rare, coming only once in a generation or so. The 1894 election, which saw enormous Republican gains, was one. It set up William McKinley's 1896 presidential victory and marked the beginning of the Progressive Era and a generation of Republican dominance. Franklin Roosevelt's 1932 victory ushered in a generation of Democratic rule and New Deal and Great Society thinking.

Ronald Reagan's win in 1980, accompanied by a stunning Republican pickup of 12 seats in the Senate to give the party control there, was another game-changer. The 1980 results showed, though, how difficult such tides are to predict. Almost no one foresaw the size of the Reagan win or the accompanying Senate takeover. Until the end, many Democrats and pundits thought Reagan too conservative for the country that was about to elect him in a landslide.

The Reagan win ushered in both 12 straight years of Republican control of the White House and a conservative era overall. In 1992, Democrat Bill Clinton took back control of the White House for his party, but that didn't stop the broader rise of both conservative sentiment and Republican strength. Two years after Mr. Clinton took office, in 1994, Republicans had one of the most-sweeping midterm elections in the last century, taking an additional 54 seats in the House and 10 in the Senate and winning control of both chambers. Mr. Clinton himself never won a majority of the national vote, and was elected in part by distancing himself from his Democratic party's traditional liberal base.

In 2006, Democrats turned around the steady rise of Republican and conservative power, but they didn't break out as a majority party. They simply moved the country to a fine balance of power between the two parties. After the 2006 election, Democrats had a majority in 25 state delegations in Congress, Republicans in 24, and one, Arizona's, was divided right down the middle.

As voters have divided power between the two parties in this way, they have also reflected their dissatisfaction with the parties by detaching from them in record numbers. That movement is best seen in the trends in party registrations.

The share of the public registered as neither Democrat nor Republican, but rather as independent, has exploded in recent years. Nationally, the share of all those eligible to vote who have registered as independent has grown to 22% from 4% since 1966, and has doubled since 1992 . . .