Definition 2 here.
Student or Learner
As the fund story broke, Nixon wondered where Ike stood. Thursday went by, and Friday. No word from the General - to the public, or to Nixon. But the Establishment was at work: the very thing that had made Nixon godd "for balance" made him unpalatable in himself, seen through Establishment eyes.
Nixon Agonistes: The Crisis of the Self-Made Man - Garry Wills - Google
In this case I believe it is the "establishment" within the Republican party. Each party has its important leaders and financiers who often call the shots, often behind closed doors.