Abstract: What role do ideologically extreme online media play in the polarization of society? Popular wisdom suggests that the internet plays a major role in influencing people's attitudes and behaviors related to politics, such as by providing slanted sources of information. Yet evidence for this proposition is elusive due to methodological difficulties and the multifaceted nature of online media effects. In this talk, I will present the results from a field experiment conducted during the 2018 U.S. midterm elections that exogenously increased exposure to online partisan media. Using a combination of survey data and web tracking data, we find immediate but short-lived increases in visits to partisan news and knowledge of recent events. However, after adjusting for multiple comparisons, we find little evidence of a direct impact on opinions or affect. Still, results from subsequent survey waves suggest that both treatments produced a lasting and meaningful decrease in trust in the mainstream media up to one year later. Consistent with the minimal-effects tradition, direct consequences of online partisan media are limited, although our findings raise questions about the possibility of subtle, cumulative dynamics.