We develop a model to analyze the political economy of media market competition in the face of imperfect mechanisms for captur- ing the return on breaking news. Media outlets face a trade-off be- tween commanding greater attention from consumers and promoting the outlet’s preferred ideological bias by suppressing unfavorable news stories. Media’s incentives to break news and to copy news stories from other outlets fundamentally diverge, leading to differences in the informational environments for their loyal readers that track the de- terminants of the outlets’ effective property rights over news stories. We show that the increase in loyal readership promotes media cover- age bias and reader polarization, and that media outlets create vicious and virtuous circles in the effects of their own coverage biases on the coverage biases of their ideologically opposite competitors. Weaker property rights over breaking news can increase or decrease polariza- tion, creating fundamentally contingent expectations for the political effects of the technological transformation of the media market land- scape.