Probably the most clear example is when a candidate travels to another country and speaks with the head of state. For example Ted Cruz traveled to Israel and Eastern Europe for his 2016 campaign. That involved of course Cruz, but also many supporting staff, not all of whom where official government officers. Its pretty common for presidential candidates to have foreign tours during their candidacy, so this happens a fair amount.

Probably the most clear example is when a candidate travels to another country and speaks with the head of state. For example Ted Cruz traveled to Israel and Eastern Europe for his 2016 campaign. That involved of course Cruz, but also many supporting staff, not all of whom where official government officers. It's pretty common for presidential candidates to have foreign tours during their candidacy, so this happens a fair amount.