Final answer:
An interest group's capability to defeat a candidate or contribute funds is indicative of its Political Action Committee (PAC), which gathers and distributes money to campaigns matching their interests.
Step-by-step explanation:
The ability of an interest group to defeat a candidate or contribute money when needed are examples of that group's Political Action Committee (PAC). PACs are instrumental for interest groups in supporting candidates sympathetic to their views and can be a crucial factor in an election. This influence is enacted by collecting money from donors and distributing it to political campaigns they support. At the same time, lawmakers often rely on interest groups and lobbyists funded by PACs for information on policy proposals and constituent perceptions. PACs can provide the means for interest groups to have a say in the political arena and to shape public policy by backing candidates who align with their interests and putting financial weight behind political campaigns.