Hillary Clinton and Donald J. Trump are in the final sprint of spending on television advertising, which has been vastly lower than in previous elections.

Mrs. Clinton’s advertising strategy has been consistent over the course of the general election, focusing primarily on Florida, Ohio and Pennsylvania. As she extends her lead in the polls, she may be looking to expand the electoral map by booking television advertising in Arizona and Texas.

Mr. Trump is also making an offensive play in the final weeks. He has $2 million of advertising booked in Virginia, a state he briefly focused on at the start of September. Mrs. Clinton has not run ads in Virginia for months, and she is ahead in the polls there by nine points.

This election year has been an interesting anomaly. Outside groups have spent far less on the presidential election this year than they did in 2012. Travis Ridout, a professor of government at Washington State University and co-director of the Wesleyan Media Project, noted that swing states were blanketed in ads four years ago. “The groups that were investing the millions upon millions in ads in highly saturated media markets just weren't happy with the returns they were getting,” he said.

Steve Passwaiter, general manager of the Campaign Media Analysis Group at Kantar Media, attributed some of the decline to Mrs. Clinton’s and Mr. Trump’s high name recognition and decades in public life. Advertising, he said, would be much more important for candidates trying to sell themselves to voters for the first time.