A key way to understanding the influence and position of different factions within the Democratic Caucus and Republican Conference in the House of Representatives is to study the major ideologically-based caucuses that almost all members join. Tracking caucuses’ members within the institution is hampered, however, by the lack of membership information in data provided by the House. Although most caucuses publish their rosters on their websites, the absence of that information in available structured member biographical data makes using it in congressional research laborious.
I recently took steps to solve this problem by manually adding caucus membership to the bioguide data available for House members from the House Clerk’s Office. The data assembled includes caucus roster memberships for the 119th, 118th, and 117th Congresses, which is as far back as available data allowed. It includes membership in the 10 caucuses: the House Republican’s “five families” (the Republican Study Group/Tuesday Group, Freedom Caucus, Main Street Caucus, Republican Study Committee, and Main Street Partnership), four Democratic caucuses (Blue Dog Coalition, Progressive Caucus, New Democrats, and Justice Democrats), and the bipartisan Problem Solvers Caucus. It can be accessed below:
Our goal in this project is to free researchers from the trouble of having to build these datasets themselves and to make the data widely available to the public as a way to understand better the factional dynamics inside the two major parties and the House. Both historically and now, the strength and weakness of competing factions have significant impact on legislative activities. Without basic data to understand the size, committee positioning, and activity of factions, this kind of analysis can be challenging.
By connecting caucus membership to members’ unique ids in the same way their district number and party affiliation is connected, this project should allow legislative data platforms like GovTrack to display it similarly. This data should enable researchers to track information like how many caucus members sit on specific committees, the caucus representation on co-sponsorships, and how caucus members voted on bills and amendments. This information can indicate the prominence of specific caucuses politically in the House, cross-ideological cooperation on specific issues, caucus legislative success, and caucus discipline in maintaining internal vote whips among others. We have shared the data with GovTrack and will work with them on integration.
This data should be considered a snapshot in time and as reliable as the lists the caucuses maintain themselves. The member bioguide data contains vacancies that have subsequently been filled in the 119th Congress and those that opened up at different times in the 118th and 117th. To access historical rosters, I used the Internet Archive’s Wayback Machine to capture information subsequently edited off the page. I accessed these rosters only on one date. Filling in a complete House roster would require accessing Wayback Machine versions to coincide with each specific vacancy cycle — work for another day. The spreadsheet provided above includes links to caucus rosters.
This data also lacks some authoritative sources. The House Freedom Caucus never has released its roster to the public. In the 119th Congress, the Republican Study Committee — the largest House caucus — decided to follow suit, eliminating the url needed to use the Wayback Machine effectively for past Congresses. The Republican Main Street Partnership did not publish a roster in the 117th Congress so it is not included in this dataset. For the HFC, I referenced Wikipedia and cross-referenced with Ballotpedia for the 119th and 118th Congresses. I relied on a Newsweek report for HFC membership in the 117th Congress. Ballotpedia referenced official rosters of the RSC for the 118th and 117th Congresses in its data tables. I carried over the RSC roster into the 119th Congress and cross-referenced membership with members mentioned in its press releases. I also found a Medium post by the Blue Dog Coalition that provided its rosters dating back to the 104th Congress.
I will present this project to the Congressional Data Task Force meeting on December 9, 2025.
