A primary focus of research on conspiracy theories has been understanding the psychological characteristics that predict people's level of conspiracist ideation. However, the dynamics of conspiracist ideation-i.e., how such tendencies change over time-are not well understood. To help fill this gap in the literature, we used data from two longitudinal studies (Study 1 N = 107; Study 2 N = 1,037) conducted during the COVID-19 pandemic. We find that greater belief in COVID-19 conspiracy theories at baseline predicts both greater endorsement of a novel real-world conspiracy theory involving voter fraud in the 2020 American Presidential election (Study 1) and increases in generic conspiracist ideation over a period of several months (Studies 1 and 2). Thus, engaging with real-world conspiracy theories appears to act as a gateway, leading to more general increases in conspiracist ideation. Beyond enhancing our knowledge of conspiracist ideation, this work highlights the importance of fighting the spread of conspiracy theories.