Presidential Partisanship and Legislative Cooperation in the U.S. Senate, 1993–2021

In this article, we detail how the rise of executive-centered partisanship has transformed president-Senate relations since 1993. We argue that the growing centrality of the president as a figurehead for their party has produced incentives for both co-partisans and out-partisans. We use a measure of presidential "success" to model variation over time and between individual senators. We show that rising presidential partisanship has increased the likelihood for out-partisans to oppose the president's legislative position, even after controlling for other markers of partisan polarization. This relationship is strongest among electorally vulnerable out-partisans. In addition, our data suggest that Republican out-partisans asymmetrically oppose Democratic presidents. We conclude that the growing centrality of the presidency in party affairs has had effects beyond administrative preemption of the legislative process; it has increasingly set a hard limit on bi-partisan cooperation on legislation and nominee confirmations in the Senate.