Undecided voters value strong personalities, don't believe that politicians are capable of solving big problems, have little information, act irrationally, and are not infrequently "crypto-racist isolationists."
I provide some excerpts below:
"These people," Jonah Goldberg once wrote of undecided voters, on a rare occasion when he probably spoke for the entire political class, "can't make up their minds, in all likelihood, because either they don't care or they don't know anything." And that was more or less how I felt before I decided to spend the last seven weeks of the campaign talking to swing voters in Wisconsin. . . .
Undecided voters aren't as rational as you think. . . . [T]here was the woman who called our office . . . [as] she had now decided to back Bush. Why? Because the president supported stem cell research. . . . one of our fellow organizers tr[ied], nobly, to disabuse her of this notion. Despite having the facts on her side, the organizer didn't have much luck.
Undecided voters . . . [are] "relatively low-information, relatively disengaged," [and] . . . view politics . . . as a chore, a duty, something that must be done but is altogether unpleasant, and therefore something best put off for as long as possible.
A disturbing number of undecided voters are crypto-racist isolationists. . . .
Undecided voters . . . have a deep skepticism about the ability of politicians to keep their promises and solve problems. So the staggering incompetence and irresponsibility of the Bush administration and the demonstrably poor state of world affairs seemed to serve not as indictments of Bush in particular, but rather of politicians in general. . . . Because undecideds seemed uninterested in assessing responsibility for the past, Bush suffered no penalty for having made things so bad; and because undecideds were focused on, but cynical about, the future, the worse things appeared, the less inclined they were to believe that problems could be fixed . . . .
Undecided voters don't think in terms of issues. . . . Occasionally I did encounter undecided voters who were genuinely cross-pressured--a couple who was fiercely pro-life, antiwar, and pro-environment for example--but such cases were exceedingly rare. . . . when I asked undecided voters what issues they would pay attention to as they made up their minds I was met with a blank stare, as if I'd just asked them to name their favorite prime number. The majority of undecided voters I spoke to couldn't name a single issue that was important to them. . . . the very concept of the issue seemed to be almost completely alien to most of the undecided voters . . . the problem wasn't the word "issue"; it was a fundamental lack of understanding of what constituted the broad category of the "political." The undecideds I spoke to didn't seem to have any intuitive grasp of what kinds of grievances qualify as political grievances. Often, once I would engage undecided voters, they would list concerns, such as the rising cost of health care; but when I would tell them that Kerry had a plan to lower health-care premiums, they would respond in disbelief--not in disbelief that he had a plan, but that the cost of health care was a political issue. It was as if you were telling them that Kerry was promising to extend summer into December. . . . Kerry ran a campaign that was about politics: He parsed the world into political categories and offered political solutions. Bush did this too, but it wasn't the main thrust of his campaign. Instead, the president ran on broad themes, like "character" and "morals." Everyone feels an immediate and intuitive expertise on morals and values--we all know what's right and wrong. But how can undecided voters evaluate a candidate on issues if they don't even grasp what issues are?
While a majority of voters are Republicans, Democrats, or are independent voters who make up their minds in a particular election contest well in advance, a significant and often decisive share, perhaps one in five or one in ten, are undecided voters who defy the models into which political scientists like to pigeonhole them.
If you trust the wisdom of crowds this may still be a wise thing, but I'm inclined instead to see it as a fundamental weakness of a democratic system of government. The problem is how to get informed and rational decision making, without systematically disenfranchising people who also have different political interests than people who would participate if efforts were made to screen for rational voters. The franchise was broadened with strong liberal support largely because no one could devise a better solution to that conundrum.