In this paper we study two measures of newspaper partisan behavior and content. The first uses explicit expressions of partisan support in the editorial section. The second is based on coverage and commentary of partisan activities, institutions and actors. We use these measures to describe the levels of relative partisan behavior during the period 1880 to 1900, and to describe changes over the period 1880 to 1980. We find that on average newspapers were initially highly partisan, but became gradually less partisan over time. Importantly, we find as much change after the 1910s as before. We investigate whether some of the common hypotheses offered in the literature can explain the changes. The initial findings suggest that these explanations can only account for part of the decline.