Americans for Prosperity spent tens of millions of dollars on the 2010 election and will spend tens of millions more this year to see conservative advocates of limited government elected — all without revealing any of its contributors. Taking advantage of a complex web of federal laws, the group, founded and financed by billionaire industrialists David and Charles Koch, has successfully kept its donors secret. But when AFP decided to wade into a Nevada Senate primary in June, it might have triggered a state law that could open its donor list to the public. In a complaint filed July 19, the Nevada Democratic Party asked Secretary of State Ross Miller to investigate whether the nonprofit organization must report the contributions it received to fund mailers attacking state Senate candidate Kelvin Atkinson, a Democratic assemblyman from North Las Vegas.