CPI:

The liberal League of Conservation Voters is fast becoming one of the nation’s strongest “dark money” forces — a realm conservative groups have typically dominated.

New documents filed with the Internal Revenue Service and obtained by the Center for Public Integrity show the nonprofit League of Conservation Voters spent a record $36 million in 2012, of which more than 40 percent — nearly $15 million — came in the form of “direct and indirect political campaign activities.”