How legislatures allocate power and conduct business are central determinants of policy outcomes. Much of the literature on parties and the committee system in legislatures examines which members serve on which committees. What has received less attention are the mechanisms by which parties allocate members to committees. I show that parties in the US Senate use matching mechanisms, like those used in school choice and the medical residency match. Republicans and Democrats use two distinct matching mechanisms, such that canonical theories of parties cannot apply equally to them. The Republican mechanism is strategyproof, whereas the Democrat mechanism incentivizes politicians to manipulate their reported preferences. Leveraging matching theory, I make theoretical predictions; corroborating them with archival correspondence and committee requests/assignments data.
