Arguments about national tax policy have taken center stage in U.S. politics in recent times, creating acute dilemmas for Democrats. With Republicans locked into antitax agendas for some time, Democrats have recently begun to push back, arguing for maintaining or even increasing taxes on the very wealthy in the name of deficit reduction and the need to sustain funding for public programs. But the Democratic Party as a whole has not been able to find a consistent voice on tax issues. It experienced key defections when large, upward-tilting tax cuts were enacted under President George W. Bush, and the Democratic Party could not control the agenda on debates over continuing those tax cuts even when it enjoyed unified control in Washington, DC, in 2009 and 2010. To explain these cleavages among Democrats, we examine growing pressures from small business owners, a key antitax constituency. We show that organizations claiming to speak for small business have become more active in tax politics in recent decades, and we track the ways in which constituency pressures have been enhanced by feedbacks from federal tax rules that encourage individuals to pass high incomes through legal preferences for the self-employed. Comparing debates over the inception and renewal of the Bush tax cuts, we show how small business organizations and constituencies have divided Democrats on tax issues. Our findings pinpoint the mechanisms that have propelled tax resistance in contemporary U.S. politics, and our analysis contributes to theoretical understandings of the ways in which political parties are influenced by policy feedbacks and by coalitions of policy-driven organized economic interests.