Mr. Obama is still investing in North Carolina and competing as intensely as ever in Florida, a state that Republicans portray as shifting into their grasp. Vice President Joseph R. Biden Jr. arrived here in St. Augustine on Saturday to rally Democrats, while his wife, Jill, visited Minnesota to guard against Republican inroads there.

Mr. Romney is still fighting hard for Ohio in the face of polls showing him lagging there, while leaving open the option of making a last-minute run at industrial states like Pennsylvania and Michigan, which have long been considered safely in the Obama column. On Saturday, he sent his running mate, Representative Paul D. Ryan, to Pittsburgh…

The candidates are set to circle each other this week through most of these states. With neither campaign taking public financing — a first since the Watergate era — both sides can afford to keep competing in all nine states judged to be most competitive and in a handful of places that could still prove to be.

“We are not seeing hard choices being made,” said Ken Goldstein, president of the Campaign Media Analysis Group at Kantar Media, a firm that monitors political advertising. “With only nine states and so much money, you may not need to make hard choices.”