The Tweed Ring spawned a vibrant financial sector that was integral to its brief success but has never been previously examined. William “Boss” Tweed and his allies employed banks controlled or comanaged by Tammany politicians to embezzle funds, build political alliances, and invest in a wide array of business ventures. The capital of these savings and commercial banks—city money, deposits from Catholic charities, and the savings of immigrant laborers—was accumulated through political channels. During their operation between 1867 and 1871, politician-bankers engaged in a mix of patronage deals and profit-driven financial speculation. In effect, Tammany banks were ground zero for the Ring's conversion of political hegemony into a windfall of economic capital that fueled party activities and buoyed personal fortunes. Importantly, the anti-Ring mobilization by upper-class reformers was more than a revolt of wealthy taxpayers concerned with abstract goals of good government or rescuing city credit; it was also a reaction by old-line bankers in direct competition with Tammany upstarts. A dramatic bank run catalyzed by reformers in November 1871 drove them into bankruptcy, bringing this novel experiment in political capitalism to an end.