The project also tracks spending, and reports show the presidential

The nearly 18,000 Senate race ads in Wisconsin were the second-highest total in the country, behind the 25,211 ads on the Montana Senate race during the first three weeks of October.

The ad data comes from reports produced by the Wesleyan Media Project at Wesleyan University in Connecticut. The ongoing tracking project is the successor to the Wisconsin Advertising Project, which ended in 2009.

The project also tracks spending, and reports show the presidential and senate races have been lucrative for local broadcasting stations and national cable networks.

From Oct 1 through Oct. 21, the presidential candidates and supporting groups spent $8.4 million on ads. That's a 92.7 percent increase over spending during the previous three-week period, which began after the Democratic and Republican national political conventions.