These days, political interest groups with names like the Coalition to Protect Seniors come with a caveat: Figuring out who’s backing them financially is nearly impossible. That’s because rulings by the U.S. Supreme Court recently made it easier for individuals, corporations, and other interests to give unlimited amounts of money to such groups so they can spend it on ads that vilify candidates with opposing worldviews. A trade association based in Virginia called Americans For Job Security, for instance, funneled some $2 million into Ken Buck’s coffers to help him beat Jane Norton during the Colorado Republican Party’s most recent primary, notes The Denver Post, which reports that since early August, about $6.5 million has flowed into Colorado’s U.S. Senate race.

While Democrat Michael Bennet is fighting to hang on to his seat, outsiders have invested more than twice the amount of cash into the race than the Buck and Bennet campaigns, ranking it the top contest in the country for such contributions.

In June, the U.S. House passed legislation that would have required more openness from donors, but the Senate killed the measure (via The Associated Press). The effects of giving without having to disclose political preferences publicly are hard to discern, but if polls are any indication, conservatives have the advantage.

Unaffiliated voters are turning their backs on Democrats, according to a 9News/Denver Post poll by Survey USA that has Buck leading Bennet 48 percent to 43 percent. Another poll by McClatchy-Marist shows Buck ahead 50 percent to Bennet’s 42 (via CNN).