Staffer on the official side and advance folks on the campaign side, almost anything the elected official sees, they have a chance to directly witness as well - or at the very least to see persons go behind closed doors. While they are assumed as loyalists for the pol, they definitely won't have the same level of attachment as a campaign advisor/deep political ally/significant other. So that also open the chance they can be the whistleblowers. By the time they realize something is dangerous it is probably already too late, they are either complicit, or is witness to career-ending type of activity. Speaking up ends their own political career as someone who can't keep secrets at a minimum. At maximum, it is definitely the kind of information people get killed for.