Committees run the agencies, but party leadership runs the committees

Weingast and Moran discussed how specific Congressional committees are the ones who have control over federal agencies. But who controls the committees and the Congressmen who make them up?  In Weingast and Marshall's paper, they assume that parties place no constraints on the behavior of individual representatives. That is objectively false. Party leadership has a similar system of rewards and sanctions that encourages their members to vote in line through threatening their probability of re-election. These fall in three main categories, the last of which is relatively new and currently evolving: 1) Committee assignment  2) Campaign funding and 3) Threat of a primary challenger.

We know elected officials have one main goal: to get re-elected. To do that, they obviously need votes, which are obtained mainly through providing benefits to their constituents and campaign funding. Constituent benefits are delivered by passing legislation favorable to your district. Being on the right committee is crucial to impacting issues important to your district. Though members state their preferences at the beginning of their term, at the end of the day, the majority party leadership determines committee assignments. The major determinant of placement has shifted from seniority to party loyalty. Those who vote against the party too often can lose their membership on valued committees, as Representative Tim Huelskamp of Kansas did in 2012 when he was removed from the budget and agriculture committees. This is why we currently see so many party line votes and why the most outspoken critics of the current direction of the Republican Party are Senators like John McCain and Jeff Flake who are not seeking re-election and thus don't face the same incentive structure party leadership relies upon to force conformity onto their members.