Final answer:
U.S. v. Nixon is considered a landmark Supreme Court case because it established that executive privilege is not absolute and can be limited.
Step-by-step explanation:
The case arose when President Nixon refused to release tapes recorded in the Oval Office, claiming executive privilege. However, the Supreme Court ruled that the need for evidence in a criminal investigation outweighed the president's claim of privilege. This decision set a precedent for future cases involving executive privilege. U.S. v. Nixon is considered a landmark Supreme Court case because it established that executive privilege is not absolute and can be limited.