It’s hard to understate just how important tax reform is to the Koch brothers, but if you asked them to finally admit that climate change is caused by humans to enact a flat tax, they wouldn’t think twice. The New York Times confirmed todaythat their preferred method of tilting the scales in their favor – the flat tax – is sure to be a major debate in the GOP primary. Ted Cruz, Rand Paul, Ben Carson, and Rick Perry all strongly support the flat tax, which the Center on Budget and Policy Priorities describes as:

“injurious to working and middle-class Americans, who would have to pay higher taxes to help make up for the massive revenue losses, face deep cuts in key programs — likely including programs such as Medicare — to accommodate the large revenue losses, or both.”

In other words, the flat tax will force low and middle-income working families to shoulder more of the burden while billionaires like the Kochs get off with paying less of their fair share. A single mother making $35,000, for example, would pay $600 more in taxes under the flat tax. Meanwhile, it provides a cover for Republicans to enact massive cuts to Social Security, Medicare, and other vital programs.

Cruz and Paul are two of the Koch brothers’ chosen five to audition for the nearly $900 million they’re spending this election cycle. The flat tax is a potent issue for candidates to highlight for the Kochs – their Americans for Prosperity has made the flat tax a cornerstone of their tax agenda. In addition to pushing it nationally, AFP also lobbies state legislatures to adopt flat taxes, as Bridge Project’s Iowa report explores.

Experts from across the political spectrum agree that a flat tax is unfair, impractical, and would demolish working families – but that hasn’t stopped Ted Cruz and Rand Paul from teaming up with the Kochs to push it through.

The question is how far right will Jeb Bush, Marco Rubio, and Scott Walker be forced to stay in the Kochs’ good graces?