Steven Spielberg’s new movie “The Post” tells the story of the Pentagon Papers from the perspective of a single newspaper. The movie focuses on Washington Post publisher Katherine Graham’s decision to publish the Defense Department’s top secret history of the Vietnam War in defiance of the Nixon administration. The stakes are high. Nixon was the first president to claim the power to impose “prior restraint” on the press — that is, to block newspapers from publishing information he deemed injurious to national security by threatening publishers with imprisonment. Once the government convinced a federal court to grant an injunction against the newspapers, those who published the Pentagon Papers could be prosecuted for criminal contempt of court. President Richard M. Nixon remains a distant and shadowy figure in the movie, his voice heard briefly in excerpts from his (then) secret White House tapes.

A spoiler, even though this is all fairly recent history: “The Post” climaxes with the Nixon administration losing a showdown with the newspapers at the Supreme Court (and offers a brief preview of the greater newspaper drama to come for Nixon, the Post and America).

The landmark First Amendment case, while profoundly important, was only the public part of the President’s reaction to the leak. Privately, Nixon wasn’t much worried about the leak of the Pentagon Papers, since the secret history cuts off in mid-1968, months before he was even elected president. Nixon was worried about something else, something that could damage him politically — the potential leak of his own Vietnam secrets.

As the Nixon tapes record, the President quickly convinced himself that the leak of the Pentagon Papers was the work of a conspiracy that intended to leak his secrets as well....

What dark secrets about Vietnam did Nixon have that he would go to such great lengths to hide? Two in particular: the Chennault Affair and the secret bombing of Cambodia....