Campaign Money Watch, which bills itself as a nonpartisan organization dedicated to improving campaign finance laws, has been particularly tough on John McCain.
The group has taken him to task over ties to the oil industry and lobbyists who have worked on his campaign. Barack Obama has hammered McCain on those issues.
Its largest donor this year is the American Federation of State, County and Municipal Employees, one of the Democratic Party's most loyal contributors. The union gave $300,000, according to the watchdog group's most recent campaign finance disclosure.
The second-largest donor is Texas billionaire David Bonderman, a significant contributor to Democrats, who has given $200,000 this year, including $75,000 three weeks ago. Bonderman is a founding partner of Texas Pacific Group, a private equity fund that holds or has held stakes in casino company Harrah's, Burger King and airlines.
