When Robert F Kennedy Jr ran for president as a Democrat in 2023, he found an unexpected ally in Scott Brown. A former Republican senator, Brown had begun a tradition of hosting Republican presidential candidates for barbecues in his New Hampshire back yard, where they could stump for votes and get attention ahead of the state’s crucial primary.

Kennedy became Brown’s first Democratic invitee. His appearance in September 2023 drew hundreds of people, Brown’s biggest crowd ever. Kennedy held Brown in such high regard that after he decided to run instead as an independent, he reportedly reached out to Brown as a possible vice-presidential running mate, though Brown declined.

Later, Brown – now running for Senate in New Hampshire – said he helped Kennedy prepare for his Senate confirmation hearings for the job of US health secretary.

Newly released records obtained by the Guardian shed further light on the men’s relationship and how Brown – who had been appointed to serve as ambassador to Samoa and New Zealand by Donald Trump during his first term – responded to a controversial trip Kennedy took to Samoa in June 2019. Months later, Kennedy’s visit would become a subject of public scrutiny when measles swept through the Pacific island nation. Samoan officials and health leaders said Kennedy, who made the trip when he was the head of a US anti-vaccine organization, bolstered the credibility of local anti-vaccine activists ahead of the outbreak, which killed 83 people, mostly children under age five.

Kennedy has said he had “nothing to do with people not vaccinating in Samoa” and that he never told anybody there not to vaccinate.