Which databases or studies track political affiliation and motive in US mass shootings?
Executive summary
A small number of public databases and research projects explicitly record motive or ideological classification for U.S. mass shootings, while many general-purpose mass‑shooting datasets focus on incident facts and only sometimes infer political affiliation; prominent examples include The Violence Project (NIJ‑supported) and specialty extremist trackers from the ADL and CSIS, but coverage, definitions and source methods vary considerably [1] [2] [3]. Researchers and fact‑checkers warn that political party affiliation is frequently unreported or unverifiable and that ideological motive is often contested, so any claim about “many shooters” belonging to one party or another should be treated skeptically [4] [5].
1. Major public databases that catalog motive or ideology: The Violence Project and related NIJ‑supported work
The Violence Project maintains a public database of U.S. mass shootings and collects psychosocial histories and motives drawn from open sources such as social media and news reporting, with NIJ support and an explicit effort to code motivations and contexts that can include ideological drivers [1]. The University of Arkansas Terrorism Research Center and affiliated scholars publish analyses distinguishing ideologically‑motivated mass shooters from other mass shooters and provide data snapshots aimed at identifying patterns in political/ideological motive [6]. Both organizations emphasize open‑source coding but also acknowledge the difficulty of definitively proving motive in many cases [1] [6].
2. Extremism and terrorism datasets that explicitly classify ideology: ADL, CSIS and similar centers
Extremism‑focused trackers like the Anti‑Defamation League’s Center on Extremism catalogue extremist‑linked mass killings and explicitly classify incidents as right‑wing, left‑wing or other ideological types, producing counts and narratives about ideological motive and trends [2]. CSIS has assembled datasets that include perpetrator ideology, group affiliation and motive for political violence, accompanied by methodology and codebooks that make their ideological classifications transparent [3]. These sources concentrate on incidents that meet threshold tests for ideological violence, so they tend to exclude non‑ideological mass murders and rely on evidence such as manifestos, statements, group ties or ideological claims to code motive [2] [3].
3. Scholarly datasets and definitions used by policy institutes
Academic and policy compilations cited by the Rockefeller Institute and other research centers build comprehensive lists of public mass shootings and use cross‑referencing protocols to determine inclusion and, where possible, motive—drawing on multiple media and archival sources to validate whether an attack was politically motivated [7]. Broad reviews of mass murderers worldwide and in the U.S. categorize motivating factors into psychological, interpersonal and political/religious motives, but show political ideology is less common in U.S. cases than in many other countries, underscoring the need for careful categorization [5].
4. Data on political signals beyond declared ideology: studies of reactions and partisan framing
Separate lines of research study how political actors and the public interpret shootings rather than the shooters’ own motives: NYU Tandon work shows political views strongly shape reactions to mass‑shooting data and how legislators post about gun policy after shootings, revealing partisan framing even when motive is ambiguous [8] [9]. Media analyses caution against the rush to assign partisan labels in high‑profile cases, arguing that politicization can outpace verified evidence about motive [10].
5. Key limitations, methodological differences and the risk of misattribution
Many datasets rely on open‑source reporting, manifestos, social media footprints or law‑enforcement determinations, and the political affiliation of shooters is often unreported or unverifiable—PolitiFact’s analysis of past claims found most shooters’ party registration or partisan identity was unknown and motive was frequently non‑political or unclear [4] [1]. Extremism trackers intentionally focus on ideologically driven violence and therefore will not reflect the larger set of mass shootings driven by personal grievances, meaning comparisons across sources require attention to differing inclusion rules and coding manuals [2] [7].
6. Bottom line for researchers and reporters: use targeted datasets and read codebooks
To study political affiliation or ideological motive, use specialized extremist datasets (ADL, CSIS) and motive‑coded scholarly databases (The Violence Project, TRC snapshots) while checking each source’s methodology and acknowledging gaps where affiliation cannot be verified; treat partisan claims reported immediately after attacks with caution and verify against dataset codebooks and law‑enforcement findings before drawing conclusions [2] [3] [1] [4].