Theories that explain the power of legislative leaders have been developed for the U.S. Congress and lower chambers of state legislatures, but they have not been tested for state senates, even though senate leaders can be quite influential. Following Mooney (2013a), I develop a new numerical index score measuring the formal power of the top chamber-elected leader of each state senate from 1995 through 2010. I then use the data to test various hypotheses explaining variation in the power of legislative leaders. The results uncover partial evidence for conditional party government theory, but only for senates that elect their own president. When the lieutenant governor serves as senate president, senators do not perceive their top chamber-elected leader as an officer able to best carry out their ideological, electoral, or policy objectives. This underscores crucial differences between senate chambers that elect their own presidents and those that do not.
