Cain, who is steadily rising in Republican primary polls on a call for tax cuts and reduced government, worked with Americans for Prosperity, the political committee founded by the Koch brothers to advocate lower taxes and spending cuts. Cain traveled the country as the group's chief spokesman in 2005 and 2006, the AP says, working alongside Mark Block, the Republican operative who is now Cain's campaign manager.

And a friend from AFP days, Rich Lowrie, inspired Cain's "9-9-9" plan for tax reform: a nine percent corporate tax rate, a nine percent national sales tax, and a nine percent flat income tax rate.