Why would a national political party that has been competitive for decades collapse overnight? In recent years, parties across Latin America went from being major contenders for executive office to electoral irrelevance over the course of a single electoral cycle. The author develops an explanation that highlights the impact of elite actions on voter behavior. During the 1980s and 1990s leaders across the region implemented policies that were inconsistent with their traditional party brand, provoked internal party conflicts, and formed strange-bedfellow alliances with traditional rivals. These actions diluted the brands of their parties, eroding voters' partisan attachments. Without the assured support of partisans, parties become more susceptible to retrospective voting. Voters who now had no party attachments deserted incumbent parties when they performed poorly. The author tests this interactive hypothesis using matched comparisons of six party-election cases from Argentina and Venezuela.