After maintaining significant regulatory constraints on financial institutions from the New Deal to the 1970s, congressional Democrats dismantled the New Deal regulatory regime for finance during the 1980s and 1990s. Why did Democrats unleash Wall Street despite a broad coalition of interest groups that opposed deregulation, and the party’s continued concern about the concentration of economic power? In this dissertation, I argue that the institutional fit between the level of centralization in Congress and concentration in the economy explain stability and change in Democrats’ position on financial regulatory policy. Centralizing institutional reforms in Congress undercut parochialism, and empowered Democratic leaders to advance the party’s collective interest by deregulating finance on behalf of American consumers and Wall Street. However, by choosing financial markets and the diffuse interests of American consumers over the “entrenched” interests of small local banks, adjacent small businesses and organized labor, Democrats significantly contributed to wealth inequality, geographic inequality, and market concentration, which in turn has resulted in political inequality and the weakening of American democracy.