Final answer:
The difficulty presidents face in the policy implementation process is described by option (C), which states that it is not easy for the president to remove professional bureaucrats when they disagree with the president's agenda.
Step-by-step explanation:
The difficulty that presidents face in the policy implementation process is described by option (C): Because of civil service laws, it is not easy for the president to remove professional bureaucrats when they disagree with the president’s agenda.
When the president appoints professional bureaucrats to carry out his policies, these bureaucrats are protected by civil service laws, making it challenging for the president to remove them if they oppose his agenda. This can create a difficulty in implementing the president's preferred policies, as the bureaucrats may impede or resist the president's instructions.
For example, if a president wants to enact a specific policy but encounters resistance from career bureaucrats who have different beliefs or interests, it becomes difficult for the president to ensure the policy is implemented as intended.