The Koch political network plans to stop running television ads in the final month before the November elections, putting its focus instead on labor-intensive field efforts to turn voters out in support of GOP Senate candidates, officials said Wednesday.

The intensification of a ground strategy is being driven by an assessment that Republicans need greater firepower when it comes to getting voters to the polls — particularly those unenthused about this year's campaign.

"We see that grassroots capabilities and the ground game is an area where we can really make an outsized impact," said James Davis, a spokesman for Freedom Partners, the network's funding arm.

The Republican National Committee recently expanded its field operation, with 1,100 paid staff now deployed across the country through the party's victory operation and GOP presidential candidate Donald Trump's campaign.

But the Koch network, which is not supporting Trump, has spent the last several years working to build a permanent ground force that can be rallied in support of conservative causes and candidates. For months, it has had 1,200 paid staffers in 36 states across its allied advocacy groups, which include Americans for Prosperity, Concerned Veterans for America, the LIBRE Initiative and Generation Opportunity. That's up from 450 four years ago, officials said.

The expanded ground force has allowed the network to dramatically increase its voter outreach. By this July, field staffers had reached as many voters through door-knocking and phone calls this year than they did in all of 2014 and 2015 combined, said Levi Russell, a spokesman for Americans for Prosperity.

Those organizers are now being trained on 5 million voters in eight states where the network is bolstering GOP Senate candidates: Florida, Indiana, Missouri, North Carolina, Nevada, Ohio, Pennsylvania and Wisconsin.

Network officials said they still plan to spend roughly $42 million on a round of TV and digital ads that is scheduled to run through early October. But they are canceling a final week of advertising they originally planned to air in Florida to support Sen. Marco Rubio, and as of now have no plans to buy more airtime after Oct. 4.

"We will still fill gaps as needed," Davis said. "But ultimately, we are going to try to double down and focus on the ground game."

The new approach comes amid a shifting Senate battleground. While network officials are confident about states such as Ohio, where Sen. Rob Portman has a large lead, they are putting new resources into North Carolina and Missouri, where the GOP incumbents face narrowing polls.