The word “bombshell” pops up a lot in “Watergate,” Charles Ferguson’s comprehensive documentary about … well, you know. From the summer of 1972, when five men were arrested breaking into the offices of the Democratic National Committee in Washington, until President Richard M. Nixon’s resignation two years later, the public was confronted with a barrage of shocking revelations. The morning papers and the evening news brought fresh reports of wrongdoing at the highest levels of government, unearthed by congressional committees, a federal grand jury and the diggings of journalists. Before the nation’s eyes, a “third-rate burglary” blossomed into a constitutional crisis.

Ferguson has given his film the subtitle “How We Learned to Stop an Out-of-Control President.” In case the implications of the lesson weren’t clear, he ends with George Santayana’s well-worn aphorism about those who don’t study the past being doomed to repeat it. Whether we are living through a sequel to Watergate — or whether out-of-control presidents after Nixon might have learned to get away with their own crimes — is in some ways an idle question. History rarely repeats itself exactly. The lessons of “Watergate” have to do with the fragility and resilience of democratic institutions, and with the stark ethical challenges that sometimes arise in political life.

Serious stuff. But the movie — more than four hours long, split into two parts with a cliffhanger in the middle — also works, perhaps unexpectedly, as escapist entertainment. Like many of my fellow citizens, I spend a lot of time thinking about the current president, whether I want to or not. He’s ubiquitous on television, in social media, and as a topic of dinner-party discourse and water-cooler hobnobbing. For the entirety of “Watergate,” however, I didn’t think about Donald J. Trump at all. I thought about Richard Nixon instead, which while not exactly pleasant was at least different.

Ferguson’s narrative is so dense and complicated, and at the same time so dramatic, suspenseful and clear, that it absorbs all of your attention. You probably know the outcome, and if you’re a history-nerd child of the ’70s like me, you’re probably familiar with many of the names and details. Haldeman. Ehrlichman. Kalmbach. Segretti. Sam Ervin. The Saturday Night Massacre. “I am not a crook.” It’s like a classic rock station on satellite radio. (The movie also has some fine musical cues of its own.)