Why do some pieces of legislation move forward while others languish? We address this fundamental question by examining the role of interest groups in Congress, specifically the effect of their legislative endorsements in Dear Colleague letters. These letters provide insights into the information that members use to both influence and make policy decisions. We demonstrate that endorsements from particularly well-connected interest groups are a strong cue for members with limited information early in the legislative process and help grow the list of bill cosponsors. As bills progress, such groups have less direct weight, while legislation supported by a larger number of organizations and a larger number of cosponsors is more likely to pass. Thus, we illuminate the usage of Dear Colleague letters in Congress, demonstrate how members use interest groups in the legislative process, and shed new light on the varying impact of groups on public policy.

Members of Congress frequently collaborate on policy initiatives, reaching out to colleagues in both parties to find common ground on solutions for the problems faced by their constituents. Using a novel dataset of over 30,000 “Dear Colleague” letters sent by members of the 111th Congress, I use the collaborative relationships that exist in the earliest stages of the policy process to measure the social influence of legislators. I demonstrate that districts represented by members of Congress who are better connected to their colleagues receive a greater share of federal grant money. I argue that this is because collaborative legislators are well‐positioned to be influential allies to strategic bureaucrats who want to maintain a broad base of support for their programs in Congress. Thus, devoting resources to building relationships with their colleagues is one way members of Congress can more effectively support the communities they represent.