["Journal of Regional Science, EarlyView. ", "\nABSTRACT\nSocial capital has long been regarded as a bulwark of democratic life. Yet in the United States—as across much of the democratic world—some of the communities with the densest social ties have proved the most receptive to antisystem politics. Drawing on county‐level data for the 2016 and 2020 US presidential elections, this paper shows that the political consequences of social capital depend on its composition rather than its volume. Bonding social capital—the formal and informal ties that hold communities together from within—is robustly connected with higher Trump vote margins. Bridging social capital —ties that connect people across socioeconomic lines—runs the other way. More strikingly, identical trajectories of local economic and demographic change pull antisystem voting in opposite directions depending on the mix of bonding and bridging ties in the area. The structure of local social relations, in short, shapes the political geography of territorial transformation.\n"]