Party Power or Preferences? Quasi-Experimental Evidence from American State Legislatures

Can majority parties control legislative outcomes by controlling the agenda, or are roll-call patterns simply the product of legislators' preferences? We argue that, holding members' preferences constant, the majority party's ability to set the agenda gives it the power to influence legislative outcomes. We present the implications of this view of party power formally and then explore them empirically in two quasi-experiments from American state legislatures. In both, agenda control varies while legislator preferences remain constant. Our consistent finding is that the majority party uses its control over the agenda to screen out bills that would split its own membership, devotes more floor time to bills that divide majority from minority party legislators, and ultimately uses agenda control to protect the policy interests of its members.