Of likely swing voters, white non-college voters are “particularly low-information voters who don’t pay attention to the daily political back-and-forth, so their opinions are driven by their economic situation,” said Jefrey Pollock, the president of Global Strategy Group, a polling firm for Priorities USA Action, a pro-Obama “super PAC.” Many, he said, are “fond of the president personally, but skeptical about their economic prospects.”

A senior Romney aide, who requested anonymity discussing strategy, says the campaign’s microtargeting has identified specific swing-voter-rich counties in swing states: In Virginia, for example, a large number of swing voters are concentrated in Fairfax County, just outside the District of Columbia; in Ohio, by contrast, undecided or persuadable voters are scattered throughout the state. In some cases, demographic patterns emerge: In Arapahoe County, Colo., just outside Denver, the majority of swing voters will probably be women, the aide said.

Among these swing voters, only some are genuinely torn about whom to support but are certain they will vote, and a significant number favor a political party and will vote for the candidate of that party or not at all.

Mr. Napier, the swing voter from Ohio, said last month that he might fall into the latter category this year, but that he did not yet have enough information to decide. Between working full time for a fabrication company and attending school part time for a degree in manufacturing engineering, he said consideration of the presidential election was an afterthought.

In 2008, Mr. Napier drew much of his information from the presidential debates, in which, he says, “McCain seemed to be distracted most of the time when he talked, and Obama seemed to be an educated man who has focus.”

Swing voters often form their opinions about candidates based on emotional intangibles and a few events, like the debates. Candidates may have just one chance to make an impression on these voters, and not always on the campaigns’ terms.

“With these voters, they’re only paying half attention, but all of these outside events have an effect,” said Neil Newhouse, the head of polling for Mr. Romney’s campaign.