The moneymen behind the outfit spending the most on the Medicare attack ads ... will not show their faces. The money is being spent through a Washington-based group, Americans for Tax Reform (ATR), that calls itself a social welfare" nonprofit, so it does not need to reveal its donors to the public. This sort of thing has been happening a lot this year in House and Senate races around the country. Candidates have found their modest war chests, filled with checks for $2,500 or less, swamped by outside groups, which have no limits on the donations they can collect. In all, more than $800 million was spent through mid-October on election ads by outside groups, according to the Center for Responsive Politics. Of that total, nearly 1 in 4 dollars is so-called dark money, meaning the identities of the donors remain a secret. Voters watching TV, listening to the radio or receiving direct-mail appeals know only the names of the front organizations that bought the ads. In the past two years, American politics has been transformed by a surge in spending. One fact tells the story: explicit political-ad spending by outside groups in 2012 is on track to double the combined total spent by outside groups in each of the four elections since 2002. Ads purchased with untraceable money tend to be among the most vicious. Nearly 9 in 10 dark-money spots are negative, and an analysis by the Annenberg Public Policy Center found that 26% of the ads are deceptive. Almost all of it - 83%, according to one review - has been directed against Democrats.