Final answer:
An exploratory committee is set up when a candidate first decides to run for office, assessing viability including fundraising and political support, before entering primary campaigns.
Step-by-step explanation:
The campaign structure that describes when a candidate initially decides to run for office is the exploratory committee. An exploratory committee is formed to determine the viability of a potential candidate's run for office. This includes assessing the political landscape, potential support, and fundraising capabilities. A successful exploratory phase can lead to the establishment of a formal campaign.
During this phase, potential candidates may conduct a range of activities such as public speaking engagements, media events, and the use of social media to gauge public interest and support.
Additionally, heavy emphasis is placed on fundraising as early contributions are often indicative of a candidate’s future fundraising success. It’s only after forming an exploratory committee and garnering sufficient support that a candidate will advance to compete in primary campaigns for the party's nomination.