WASHINGTON -- The race for a newly drawn congressional district in California's Inland Empire is shaping up as a clash of titans. It's not the candidates -- Republican Rep. Gary Miller and his leading Democratic opponent Pete Aguilar -- who are making a splash at the moment, but rather two powerful interest groups, the National Association of Realtors and the California & Nevada Credit Union League, who are investing big money to support candidates that have long backed their interests.The contest in California's 31st District has seen the most spending from independent groups of any non-special election House race in the 2012 election cycle.