Americans for Prosperity (AFP), the flagship political arm of the rightwing network formed by the fossil fuels billionaire Charles Koch and his late brother David, is launching a multimillion-dollar campaign backing Donald Trump’s plans to extend tax cuts and roll back federal regulations.

A private fundraising letter from AFP to its secretive list of donors, seen by the Guardian, outlines the organization’s strategy for the first six months of the new Trump administration.

The eight-page document, made public here for the first time, promises a “herculean undertaking” in which AFP says it will press for renewed and deepened tax cuts and an “unwinding [of] as many of the growth and innovation killing regulations as possible”.