In June 2014, the EPA released its proposal for rules to regulate carbon dioxide emissions from existing fossil fuel power plants, triggering considerable debate on the proposal’s environmental and economic consequences and on alternatives highlighted by the proposal and by other stakeholders. One question not addressed by this debate is this: What if the EPA regulations turn out to be inadequate to address future mitigation goals? That is, what will the landscape for future policies look like if these regulations turn out to be just an interim measure? This analysis explores the long-term consequences of several key regulatory design choices, including mass-based versus rate-based standards, tradable versus non-tradable standards, and differentiated versus single standards. It finds that these consequences may be significant: differentiated standards lead to relatively greater investment in coal retrofits; non-tradable standards lead to relatively greater retirement of coal capacity. It may be the case that key policy choices entail one set of tradeoffs if proposed EPA rules are viewed as relatively permanent and final and another set of tradeoffs if the rules are viewed as an interim solution.