Final answer:
The correct answer is option B) Senate Majority Leader.
Step-by-step explanation:
Struggles to secure the loyalty of moderate Democratic members on significant votes regarding economic recovery and health care reform most likely refer to the role of the Senate Majority Leader(B). This individual is tasked with leading the majority party in the Senate and has various tools at their disposal to ensure party members vote in line with party interests.
This role is crucial, especially when pursuing legislative goals set by the President, as achieving a supermajority of 60 votes is often required to overcome a filibuster in the Senate.