What government action initially prevented newspapers from publishing the Pentagon Papers?

The correct answer is based on the concept of prior restraint, which refers to government actions that prevent material from being published, rather than allowing it to be published and then punishing for any potential transgressions afterward. In the case of the Pentagon Papers, the Nixon administration attempted to stop the New York Times and other newspapers from publishing the classified documents regarding the Vietnam War by arguing that their publication would cause irreparable harm to national security. This action was a clear attempt at prior restraint, as it sought to inhibit the media's ability to disseminate information before it was published, rather than responding to it after it had been made public.

Prior restraint is a significant issue in First Amendment discussions because it raises questions about the balance between national security interests and the freedom of the press. The courts ultimately ruled against the government's attempt at prior restraint in the case of the Pentagon Papers, affirming the right of the press to publish information, even when it concerns sensitive topics such as national security.

Understanding this context highlights why prior restraint is the most appropriate answer, as it encapsulates the fundamental issue at stake in this legal and constitutional conflict.