The Republican donors who have financed the party’s vast outside-spending machine are turning against the consultants and political strategists they once lavished with hundreds of millions of dollars.

In recent months, they have begun holding back checks from Republican “super PACs” like American Crossroads, unsatisfied with the groups’ explanations for their failure to unseat President Obama or win back the Senate. Others, less willing than in the past to defer to the party elders and former congressional staff members who control the biggest groups, are demanding a bigger voice in creating strategy in exchange for their continued support.

Donors like Paul Singer, the billionaire Republican investor, have expanded their in-house political shops, building teams of loyal advisers and researchers to guide and coordinate their giving. And some of the biggest contributors to Republican outside groups in 2012 are now gravitating toward the more donor-centric political and philanthropic network overseen by Charles and David Koch, who have wooed them in part by promising more accountability over how money is spent.

“People are really drawn to the Koch model,” said Anthony Scaramucci, a New York hedge fund investor and Republican fund-raiser, who attended the Kochs’ annual donor conference near Palm Springs, Calif., in January. “It’s adaptive, data-driven, and they are the most propitious capital allocators in political activism.”