In the U.S. Congress, the responsibility for proposing legislation primarily lies with members of Congress, which includes both Senators and Representatives. Any member can draft and introduce a bill, but it often requires input from various stakeholders, including constituents, advocacy groups, and party leadership. Additionally, committees play a crucial role in shaping legislation, as they review, amend, and recommend bills for consideration by the full chamber. The legislative process is thus a collaborative effort, with individual members advocating for their proposed laws.