Probably the "independent voter" no longer exists, which is why the phrase needs quotation marks. Undecideds are just that: undecided.
According to the Elizabeth Kolbert, writing in the New Yorker, Stephen Colbert sees them as "people who don’t think about what they want until they get right up to the register at McDonald’s." Apparently a couple of political scientists who have studied this group sees them that way, too.
Two political scientists, Larry Bartels, of Vanderbilt University, and Lynn Vavreck, of U.C.L.A., recently tried to figure out who those few voters still up for grabs actually are. They sifted through multiple surveys, involving a total of ten thousand respondents, and came up with a sample of five hundred and ninety-two people who truly seemed undecided. Bartels and Vavreck determined that only thirty per cent of the undecideds were genuine Independents, while forty per cent lean Democratic and slightly more than twenty per cent lean Republican.
Undecided voters tend to get a bad rap. “To put them in perspective,” the author David Sedaris wrote in Shouts & Murmurs shortly before the election of 2008, “I think of being on an airplane. The flight attendant comes down the aisle with her food cart and, eventually, parks it beside my seat. ‘Can I interest you in the chicken?’ she asks. ‘Or would you prefer the platter of shit with bits of broken glass in it?’ ” ...Elizabeth Kolbert, New Yorker
Sedaris pretty much nails it.