In young democracies with weak parties, there is some evidence that partisan identification may shift in response to short-term government performance. The massive protests that erupted in Brazil in June 2013 sharply increased the salience of, and public attention to, poor government performance and took most observers by surprise. They were also widely depicted as nonpartisan or even antipartisan. We use two well-timed surveys to examine the effects of the protests on mass partisanship. We find that the protests led to increased nonpartisanship and decreased attachment to the governing Partido dos Trabalhadores (Workers’ Party, PT) among the public as a whole. We also show that small leftist parties were more broadly represented among protesters than has been previously recognized.