which would most likely hold a fundraising campaign to elect a pro - gun senator?\no a chamber of…

Brief Explanations:

Special - interest groups advocate for specific issues. A pro - gun special interest group would likely hold a fundraising campaign to elect a pro - gun senator to further their cause. Chambers of commerce focus on business - related issues, a random group of individuals may not have the organization, and while political parties may have stances on gun issues, special interest groups are more single - issue focused on this matter.

Answer:

a special interest group