What should Mr. Tully's daughter be authorized as to handle his Medicare enrollment?

To effectively manage Mr. Tully's Medicare enrollment, his daughter must be legally authorized to act on his behalf, which is why the correct answer focuses on the necessity of formal legal authorization. This can be accomplished by having either a court-appointed legal guardian or holding a power of attorney, which specifically designates the daughter the authority to make decisions regarding Medicare enrollment and benefits.

The requirement for formal authorization is critical as Medicare regulations and processes need to be conducted by individuals with legal standing to ensure accountability and compliance with privacy laws, such as HIPAA. Without proper legal authority, any actions taken by a family member could be deemed invalid, risking potential delays or complications in Mr. Tully's enrollment or access to necessary medical services.

In terms of the other choices, while family members often play essential roles in assisting with healthcare decisions, simply being a family member does not confer the necessary legal authority to manage Medicare enrollment. An informal oral agreement lacks the legal backing needed in these situations, and variations in state laws do not uniformly allow any family member to enroll someone else, further underscoring the importance of having established legal authority.