Yesterday, The Guardian published roughly 1,500 pages of documents from an investigation into whether Wisconsin Gov. Scott Walker illegally coordinated with conservative non-profit groups in an effort to get around campaign finance laws while fighting against recall elections in the state during 2011 and 2012.

The investigation effectively ended in 2015 when the Wisconsin Supreme Court ruled that it was not illegal for “issue” groups and campaigns to coordinate, but prosecutors have appealed to the U.S. Supreme Court, which is expected to announce in the near future whether it will hear the case. In their petition to the U.S. Supreme Court, the prosecutors argued that two of the Wisconsin Supreme Court justices should have recused themselves from the case because their own elections benefited from the work of the Walker-allied groups. The documents obtained by The Guardian include evidence about the role those groups played, including an e-mail from Gov. Walker describing one of them as “the key to retaining” Justice David Prosser.

The documents reveal political fundraising in stark detail and open a rare window into how money works its way into the political system, especially through tax-exempt social welfare organizations that can spend millions to influence elections without disclosing their donors. Below are the five money-in-politics lessons CREW identified in a review of the documents.