Since 1979, one in every six South American presidents has failed to complete his constitutional term. These presidential failures' occur when elected presidents are forced out of office but without compromising the democratic order. This article seeks to discover the factors that underlie presidential failures through a survival analysis of 65 South American presidencies between 1979 and 2012. We argue that democratic stock', assessed by taking a historical perspective on democracy, significantly affects presidential survival, a finding which has not been observed in previous studies. It is found that partisan support and democratic stock reduce the hazard of presidential failure. Surprisingly, inflation, executive-legislative power imbalances, party system fragmentation and presidential scandals have no significant effects. These findings offer new evidence for the institutions vs. street' debate by showing that, when institutional variables are accounted for, the effect of social mobilisations significantly weakens.