Final answer:
The federal government entity least subject to the revolving door phenomenon is the courts, due to life terms for judges and less public and electoral pressure.
Step-by-step explanation:
The part of the federal government that is least subject to the revolving door phenomenon is the courts. The revolving door phenomenon refers to the movement of personnel between roles as legislators and regulators and the industries affected by the legislation and regulation.
In the context of the federal government, the judicial branch, and particularly the courts, is the least impacted by this because judges and justices are appointed for life terms, removing the incentive to cater to future employers. Moreover, the courts are often less in the public eye compared to other branches of the government and are not subject to electoral pressures.