Recent research builds on the observation that democracies have more durable alliances to argue that democracies make more reliable allies. This need not be the case. Alliances serve as commitment devices, adding ex ante credibility to states' claims about ex post behavior. Variation in alliance durability must reflect differences in the desirability of formalizing alignments. Put simply, democracies are "most improved" by formal commitments. We offer two related explanations for why democracies might actually be less reliable alliance partners. Information costs for participating in policymaking and the advantages of organized interest groups combined with distributional incentives generated by the periodic turnover of governments may conspire to make informal commitments on the part of democracies problematic. Determining the net effect of democratic virtue and vice is best done empirically. We test alliance reliability by focusing on intervention, rather than on the duration or the number of commitments. Our results suggest that democracies make less reliable allies.