Final answer:
An attorney has a duty of loyalty to their client, ensuring advice and representation are conflict-free, as established by cases like Glasser v. United States and Strickland v. Washington, to adhere to the Sixth Amendment.
Step-by-step explanation:
An attorney has a duty of loyalty to protect the client and to ensure that the client receives advice and representation that is free of conflicting interests. This principle is rooted in the ethical standards that govern the legal profession, which require that lawyers avoid conflicts of interest to provide the most effective and dedicated representation to each client.
Cases such as Glasser v. United States highlight the importance of this duty, noting that a conflict of interest in representing co-defendants can violate the Sixth Amendment's Assistance of Counsel Clause. The Strickland v. Washington case further sets an objective standard of reasonableness for counsel's performance, emphasizing the necessity for competent legal representation without conflicts that could adversely affect the outcome of a case.