Which case determined that actual malice must be proven for a libel lawsuit against the press?

The case that determined that actual malice must be proven for a libel lawsuit against the press is New York Times Co. v. Sullivan. This landmark Supreme Court decision established the standard of "actual malice," which requires that a public figure must prove that the press published false information with knowledge of its falsity or with reckless disregard for the truth. The ruling was significant in protecting freedom of the press and ensuring that robust debate and dissemination of information could occur without the fear of frivolous lawsuits.

This standard was set to uphold the First Amendment rights, providing the press with greater latitude to cover public figures and issues without the threat of legal repercussions, thus fostering an environment for open discourse in a democratic society. Other cases listed, such as Regents of the University of California v. Bakke, Plessy v. Ferguson, and Citizen's United v. Federal Elections Commission, tackle different constitutional issues and do not pertain to the standards of libel against the press.