The network run by conservative billionaire brothers Charles and David Koch is refocusing its efforts in competitive Senate races in Pennsylvania, Indiana, North Carolina, and Missouri, according to reports. 

The Kochs are shifting away from television ads and instead encouraging supporters to contribute to groups to boost field programs to turn out voters, CNN reported. 

“In January, if you said to us: ‘Would you be in North Carolina?’ You’d rather hope that would not be necessary,” said Tim Phillips, president of Americans for Prosperity, a conservative advocacy group backed by the Koch brothers.  

The Koch network is reallocating money to North Carolina and Missouri to support Republican incumbents facing surprisingly strong Democratic challengers. Phillips said the North Carolina buy for Sen. Richard M. Burr could be interpreted as an “abundance of caution.”

[Roll Call Election Guide: Ratings for Every Race in the Country]

Based on new polls that show other Republican incumbents pulling away from their challengers, the network is cutting $500,000 planned for Sen. Marco Rubio in Florida and has already cancelled ad slots for Sen. Rob Portman in Ohio. 

The Koch network has no plans to air any TV ads after Oct. 5. 

Given the shift away from TV ads and toward direct mail and knocking on doors, their super PAC, Freedom Partners Action Fund, is not expected to file a strong haul in its August fundraising report due Tuesday.