Committee members, some of whom are vaccine skeptics, are likely to recommend restricting the use of the shots at birth or delaying them until later in childhood.

The two agents’ accounts offer an inside view of a bureau buffeted by politics and upheaval, adding to the scrutiny of the F.B.I. director as he prepares to testify to Congress.

His knowledge of the ways cameras and media create narratives helped him redirect those stories in service of larger causes like environmentalism.