The vast majority of voters decided long ago whether they would back President Obama or Mitt Romney in November. But not everyone is so sure. Despite an avalanche of ads, polls suggest that anywhere from 2 percent to 10 percent of the 130 million people expected to cast ballots can't seem to make up their minds. Stephen Colbert joked that "the fate of our country is now in the hands of people who don't think about what they want until they get right up to the register at McDonald's," says Doyle McManus at the Los Angeles Times. But obviously, it's more complicated than that, and with the rest of the electorate pretty evenly split, both campaigns are waging intense campaigns to win over the undecideds. With the election less than two months away, why are these voters still on the fence? Here, four theories:

1. Bafflingly, they still don't understand the candidates' policies
There are huge issues at stake in November — wars, the $16 trillion national debt, health-care reform, unemployment, says Armen Gabrielian at If you're paying attention, you can't possibly be confused "at this late stage" about the differences between the candidates on, say, Iran — which Romney wants to bomb and Obama doesn't. Clearly, "these undecided voters are simply ignorant of what the positions of the candidates are." And Romney's not helping with his vagueness on how cutting waste, fraud, and unnamed tax loopholes will close the deficit, or what he means to do with his "preposterous," gigantic defense budget.

2. They don't like either of their choices
Some people just don't like the idea of voting for Obama or Romney, says Amanda Paulson in The Christian Science Monitor. Take Julia Wrapp, a Colorado real estate agent and entrepreneur who voted for Obama in 2008, but is on the fence this year. She's "neither apathetic nor uninformed." She's not happy with how Obama has handled the economy, but isn't sure Romney has the vision and integrity to do better. So she has to figure out which candidate she dislikes less: "I'd vote for Obama because I'm not sure I trust Romney. I'd vote for Romney because I'm not sure Obama can handle the job." Plenty of voters, says McManus, are "genuinely torn."

3. They like Obama, but not his record
Polls show that plenty of undecided voters like Obama personally, says Jim Geraghty at National Review. It's just that when they're asked to "name something President Obama has done in office that they like, they gave him credit for trying," but draw a blank. For now, the perception that Obama is warm, the kind of guy you wouldn't mind having a beer with, is keeping him afloat. But it hasn't been enough to persuade skeptics that he deserves a second term.

4. They know how much is riding on their decision
With Romney and Obama neck-and-neck, says Patrik Jonsson at The Christian Science Monitor, the presidential race hangs on the undecided voters in maybe a half dozen battleground states. That's a lot of responsibility for a group of fewer than 1 million people. These voters — the "persuadables" — are less partisan than most of us, and always wrestle with complex, shifting personal alliances and sympathies. This time around, "their struggles to come to a decision are compounded by a sense that they, more than other voter subgroups, could have a real effect on America's future."

Read more political coverage at The Week's 2012 Election Center.