Conservative donor David Koch in a 2013 file photo. The political network he and his brother, Charles, have created is not backing Donald Trump's presidential bid this year. (AP)
Four years after Charles and David Koch's political network opened its bank accounts to promote Republican nominee Mitt Romney, it's now spending millions to save the Republicans' Senate majority from their presidential candidate.
This year's Senate ads will focus on issues involving the candidates, not national issues, said James Davis, spokesman for Freedom Partners Action Fund, a superPAC that is doing most of the network's TV ads.
Most of the ads deal with "cronyism and corporate welfare, and/or spending and government over-regulation," Davis told NPR in an interview. "What we see is that there's not a national issue per se that is mobilizing voters or that voters are encouraged or discouraged about."
This strategy marks a reversal from 2012, when Koch ads hammered at Obamacare and other Washington controversies. The network spent $78 million on general-election presidential advertising, according to the Wesleyan Media Project, which tracks political advertising.
The Koch network accounted for 92 percent of the spending by all conservative outside groups in the Obama-Romney fall campaign.
This time around, the network isn't doing anything to help Trump.
In Pennsylvania, where first-term Sen. Pat Toomey is now trailing Democrat Katie McGinty, Koch groups have spent at least $3.5 million, or half of the total conservative spending, according to federal records analyzed by the Center for Responsive Politics.
That's how the Democrats are playing it — making sure to keep Trump in the debate. Sadie Weiner, spokeswoman for the Democratic Senatorial Campaign Committee, said the Kochs' Trump-free strategy won't work.
"The Republican senators who they're advertising for and spending tens of millions of dollars for, are pretty much unanimously standing with Donald Trump," she said.
Most of those endorsements have been pretty tepid, but still warmer than the relationship between Trump and the Koch brothers.
Trump tweeted a year ago that his primary rivals might be Koch "puppets."
Charles Koch, interviewed by ABC News in April, could hardly have sounded more appalled by Trump's idea to make Muslims register with the government.
"That's reminiscent of Nazi Germany. I mean, that's monstrous," he said.
But the Koch network wouldn't go with Hillary Clinton
"We do not like Ms. Clinton's record," said Tim Phillips, president of Americans for Prosperity. "Clearly, on the issues that matter to us, she's just a disaster."
Americans for Prosperity is the network's main organization for ground operations. Phillips said it has about 700 paid staff in 35 states, plus volunteers.
"We think we can make the biggest difference by focusing very specifically on the issue differences between these Senate candidates," Phillips said.
"The presidential race will absolutely buffet and have an impact on these Senate races. We're just not going to get involved in it."