In 1992, the political scientist Raymond E. Wolfinger of the University of California (Berkeley), along with five of his students, published The Myth of the Independent Voter, a book that posed a challenge to—well, to people like me. For some time, I've been saying that the key to American politics is in the center. Independents make up about a third of the electorate, yet are neglected by the two increasingly extreme major parties. Whichever party manages to dominate the center without losing hold of its partisan base will be the majority party, possibly for years to come. Or so I've claimed.

One problem with my view is this: Party leaders aren't idiots. Why would they neglect this vast independent center if it is up for grabs? Various answers suggest themselves (for example, primary elections are dominated by fierce partisans who prefer extreme candidates), but another answer is possible. Perhaps independents are not really up for grabs.

Wolfinger and his colleagues took a closer look at independents in presidential elections from 1952 to 1988, using data from the University of Michigan's biennial American National Election Studies. Like many polls, the ANES survey asks respondents to identify themselves as Democrats, Republicans, or independents; but then it goes on to ask Republicans and Democrats whether their party identification is strong or not very strong, and to ask independents whether they think of themselves as closer to the Republicans or the Democrats. It thus shows seven degrees of partisanship, instead of the usual three groups.

Mining the ANES data, Wolfinger and company found that most people who identify themselves as independents are not uncommitted swing voters. Rather, "they are largely closet Democrats and Republicans." Indeed, they vote much as weak partisans do. They may be independent identifiers, but they are mostly not independent voters.

Two polarizing presidents later, is that still true? With the help of Mark Hiller and Thomas Mann of the Brookings Institution's Governance Studies Program (where I am a guest scholar), I took an updated look at the ANES data for presidential elections through 2004. The charts included here illustrate the findings.

The chart on the facing page shows how Americans have categorized their party ties since 1952. The deeper the color, the stronger the partisanship. Pure independents are the white band in the middle.

primary sources chart

The first finding that pops out is the basic stability of the country's partisan structure over more than five decades. The data show no major disruptions, though the triumphs of LBJ in 1964 and Ronald Reagan in 1984 are evident. The number of true independents has grown, but only to 10 percent of the electorate. They remain the smallest of factions.

Despite their party's current gloom, Democrats (strong and weak) still outnumber Republicans (strong and weak) by 33 percent to 28 percent, as of 2004. And many weak Democrats have been replaced by independents who lean Democratic, so the blue universe—everyone who either identifies or leans Democratic—has shrunk less than it otherwise might have.

Republicans, however, have narrowed the gap. The red universe has expanded, mostly at the expense of weak Democrats. Moreover, Republicans, though outnumbered, punch above their weight. The reason is turnout. In the ANES surveys, Republicans report voting at higher rates than Democrats, and strong partisans report voting at higher rates than weak partisans—both tendencies that favor Republicans. The turnout rates for partisans and leaners have not changed much since the 1960s. But something that has changed—a lot—is the voting rate of true independents. Their turnout has plummeted by about 30 percentage points since the late 1950s.

The second chart, on this page, suggests why. It shows the percentage of people in each category of partisanship who told the ANES in 2004 that one of the parties represented their views "reasonably well." Think of it as an alienation index. The more partisan you say you are, the more likely you are to feel that one of the parties speaks for you. Fewer than half of true independents feel represented by a party, which presumably is why their turnout is so low. They don't like what's being offered.

primary sources chart

Notice that the graph is not symmetrical. At every level of partisanship, the red universe feels better represented than does the blue universe. Republicans, it appears, have the stronger and more appealing brand. They are doing a better job of explaining what it means to be a Republican and why voters should care. Democrats seem to have a "mushy brand" problem. They are Chevrolet to Republicans' BMW or Jaguar.

That hunch is supported by the fact (not illustrated here) that Republicans are more ideological than Democrats—or, from an alienated independent's point of view, more extreme. By a margin of about 20 percentage points, Republicans (strong and weak) are more likely to call themselves conservative than Democrats (strong and weak) are to call themselves liberal.

Put those facts together, and they add up to Republicans' making up in passion and turnout what they lack in numbers. Meanwhile, true independents, most of whom identify themselves as moderates, sulk at home on Election Day, thus diminishing their influence and deepening their funk. A sorry state.

The crucial political question, of course, is not how all of these partisans and independents identify themselves, but how they vote. The third chart, on the next page, provides the answer, for the five most recent presidential races in which no major independent candidate was running (so you can assume that a low vote for one presidential candidate equals a high vote for the other).

primary sources chart

Over almost 30 years, the picture is once again strikingly stable. And it is not ambiguous. What Wolfinger found in 1992 is still true: Independent leaners vote like weak partisans. Only true independents split their vote or swing.

A closer look at this chart reveals a few interesting details. First, the Democratic universe used to vote less loyally than did the Republican, but by 2004 the loyalty gap had pretty much closed. For that, Democrats can thank the Great Divider, President Bush.

Second, and more surprising: Democratic-leaning independents are usually more partisan in their voting behavior than are weak Democrats. Or perhaps, on reflection, this is not so surprising after all. Remember, some components of the traditionally Democratic base, such as union members and blacks, tend to be socially conservative, while many college-educated independents turn up their noses at partisan labels but are consistently liberal in outlook. (As the chart shows, Republicans once exhibited a similar confusion, but by 2004 they had aligned party affiliation with ideology. In time, Democrats will likewise sort themselves out.)

Finally, look at true independents. Since 1984, they have moved toward the Democratic column by a whopping 30 points, with an especially large lurch toward Sen. John Kerry, D-Mass., in 2004. Yet, over the same period, independents have grown less liberal and more moderate. Why, then, are they turning blue? The fierceness of the Republican base seems to have repelled them. Polling in 2005, after the ANES data came in, has shown independents' support for Bush and the Republicans continuing to crumble at an alarming pace. Republicans' edge-oriented strategy has not come without cost in the center.

Republicans might say, So what? With their small share of the population and smaller share of turnout, true independents are in no position to swing any but a close election. To judge by the ANES data, the idea of a quiet mass of independent swing voters waiting to be mobilized is the pipe dream of wishful moderates. Like me.

Or maybe not. Some independents surely are "closet partisans," as Wolfinger and his colleagues say. But others are, as it were, closet moderates, holding their noses while voting for the ideologically nearer of two distastefully distant extremes.

What we do not know is how they might vote—or how many more of them might vote—if the general election ballot offered them a major-party candidate with broad centrist appeal: say, Sen. John McCain, R-Ariz., who so galvanized independents in 2000. Had he won the Republican nomination, those independents might well have given him a thumping victory over Vice President Gore.

Remember, too, that public opinion in the center has been unled and disorganized for years. As Prime Ministers Ariel Sharon and Junichiro Koizumi have so impressively shown in Israel and Japan, vigorous leadership can create a dynamic center as well as mobilize one.

But without centrist candidates, there can be no centrist voters. For now, Republicans have the advantage of a strong brand and a passionate following. But the Democrats are winning in the center even as their support among their partisans firms up. And it is they, with their large numbers and lagging motivation, who have the greater potential to make gains in turnout and commitment. If the Democrats ever manage to revive their brand, watch out.