“Personality does matter,” said Michael Dee, a lawyer in West Des Moines. “Because this person is going to be on TV all the time as president.”

The emphasis on character and personality is not accidental; to some degree, candidates deliberately play up elements of their lives that appeal to conservative voters, especially when compared with the personal lives of their rivals.

Mr. Romney has rolled out a series of television commercials narrated by Ann, his wife of 42 years. Mrs. Bachmann rarely misses a chance to talk about raising her foster children. And Rick Santorum, the former senator from Pennsylvania, has put photographs of his seven children on political brochures, with this detail: “Rick and his wife, Karen, have home-schooled each of their children.”

That last fact was well known to Dwayne Kriegel, a postal carrier in Grinnell, who is backing Mr. Santorum in the caucus on Tuesday. “He’s passionate about his dedication to family values,” Mr. Kriegel said. “The others say what they think the voters want to hear, while he lives it.”

Those interviewed were equally as outspoken about what qualities repel them. Phil Dillingham, 62, a retired manager at Ford Motor Company who lives in Moultonborough, N.H., said he could never vote for Gov. Rick Perry of Texas, because of what he called the candidate’s swagger.