ThinkProgress has another installment in its investigation, in which they look at the ties between the Chamber and Karl Rove's Crossroads GPS, an offshoot of American Crossroads.

Now, a new investigation by ThinkProgress details just how intertwined the two groups are in their quest to advance a conservative political agenda. At every turn, from the operatives running the two organizations to their targeted races to their media firms, American Crossroads and the U.S. Chamber of Commerce are bound to one another. Prior to becoming President and CEO of American Crossroads, Steven Law served as chief legal officer and general counsel of the U.S. Chamber of Commerce. His duties included personally overseeing the legal side of the Chamber’s multimillion-dollar political program.

Similarly, the man currently in charge of the Chamber’s political activities, Bill Miller, has a history with Law and Rove. In April, the three met along with other GOP consultants, to coordinate how to jointly fight Wall Street reform. The very next day, Miller sent out an e-mail directing all Chamber members to fight reform and Rove appeared on Fox News to peddle his theory that the Wall Street reform bill would result in the government snooping into "everybody’s checking account."

In addition to the cooperation between top operatives, the two groups have exhibited uncanny coordination in their election targeting. In a number of Senate races, the Chamber and American Crossroads coordinated their advertisements – one group put up ads in a race as the other group pulled its own down – in order to ensure attack ads were always running against the Democratic candidate....

Together, the the Chamber-Crossroads Alliance account for $127 million in planned spending this election, nearly one-third of the $400 million total pledged by outside conservative groups. But until Congress passes sensible campaign finance reform, we will never know exactly who – or which country – is funding their political attack ads.