The mechanisms by which users of platforms such as Facebook and Twitter spread misinformation are not well understood. In this study, we argue that the effects of informational uses of social media on political participation are inextricable from its effects on misinformation sharing. That is, political engagement is both a major consequence of using social media for news as well as a key antecedent of sharing misinformation. We test our expectations via a two-wave panel survey of online media users in Chile, a country experiencing information disorders comparable to those of the global North. Analyses of the proposed and alternative causal models with two types of structural equation specifications (fixed effects and autoregressive) support our theoretical model. We close with a discussion on how changes in the way people engage with news and politics - brought about by social media - have produced a new dilemma: how to sustain a citizenry that is enthusiastically politically active, yet not spreading misinformation?