Dark Money Dominates Political Ad Spending

Presidential candidates, congressional hopefuls and the super-PACs that back them are preparing to disclose to voters Jan. 31 who has been providing the tens of millions of dollars they have poured into political ads. There's one hitch: that's only about a third of the money that's been spent shaping the elections.

The rest comes from so-called dark money groups—social welfare organizations, associations and others—which aren't required to reveal the interests behind them and have put up more than $213 million on political ads since the start of 2015, an analysis of Kantar Media CMAG data shows. The groups have promoted their views on everything from climate change to health-care policy to immigration. Official campaigns and super-political action committees have spent about $114 million.