But it is not clear that Mr. Cain, 65, has any particular plan to seize this moment, beyond using the attention to sell books. Like the other candidates vying to become credible alternatives to Mr. Romney and Mr. Perry, Mr. Cain is operating on a shoestring. He raised $2 million last spring. More money is coming in, he said, and he has 40 staff members, mostly in Southern states. Still, an adviser to the campaign said the campaign had only four people working in Iowa, and there is no plan to change strategy.

Many Republicans doubt this will be enough to launch Mr. Cain in the crucial early states, especially if he decides to avoid retail politics.

“No candidate can afford to spend two or three weeks not being in New Hampshire this year,” said Steve Duprey, a Republican National Committee member from the state. “He has not made as much progress organizing in New Hampshire as he could have, but there’s time.”

When asked why he would launch a book tour while running for the presidential nomination, Mr. Cain said that “the two complement one another” and that the benefits go beyond raising his name recognition among voters — one of his main goals.