The Bipartisan Campaign Reform Act (BCRA) of 2002 was the first major change in US federal campaign finance law in a quarter of a century. Many attempts at reform had failed in that period. Few members of Congress were enthusiasts for reform, the two parties and two chambers had conflicting interests to protect, successive presidents did not promote the issue and public pressure for reform was weak. When reform was achieved in 2002, many of these formidable obstacles remained in place. This paper draws on the literature of public interest reform and policy innovation to attribute the change to a policy entrepreneur whose resources had undergone a sharp increase, the neutralization of opposition, the impact of an event (the bankruptcy of the Enron Corporation) and membership turnover in Congress. The substantial support for the bill in Congress from Democrats, the party with most to lose from reform, is attributed to the inescapability of past commitments.