• **Congress.gov API v3** — Bill text, member profiles, committee assignments, votes, nominations, treaties. The official Library of Congress legislative database.
• Voteview — DW-NOMINATE ideology scores for every member since 1789. Produced by UCLA political scientists.
• Senate Lobbying Disclosure Act (LDA) — Quarterly lobbying filings showing which firms, clients, and issues received lobbying activity. Filed directly with the Senate.