Final answer:
An iron triangle offers a federal agency the advantage of establishing supportive relationships with both members of Congress and interest groups, nurturing policy support and agency agendas.
Step-by-step explanation:
The advantage of an iron triangle for a federal agency is that it provides the agency with allies in Congress as well as in the private sector. An iron triangle is a term used to describe a stable, mutually beneficial relationship among a congressional committee, an interest group, and a federal agency. This arrangement allows an agency to align with lawmakers who can secure funding and policy support while working with interest groups that offer expertise and promote agency agendas. This collaborative relationship fosters a sense of mutual support and policy continuity.