Less than a year from now, the presidency of George W. Bush will end, but the consequences of Bush's policies and the arguments about them are likely to be with us for a long time.
As Jan. 20 draws near, there is an evident temptation, among journalists as well as politicians seeking to replace Bush, to close the book and move ahead. It's an impulse that makes the existence of documentaries like Alex Gibney's "Taxi to the Dark Side" all the more vital. If recent American history is ever going to be discussed with clarity and ethical rigor, this film will be essential.
Gibney directed "Enron: The Smartest Guys in the Room" and was an executive producer of Charles Ferguson's "No End in Sight," films that show the same combination of investigative thoroughness and moral indignation that animates "Taxi."
The germ of this documentary's story is the case of Dilawar, a taxi driver who was detained in Afghanistan in 2002 and who died in American custody at the prison in Bagram a few months later.
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Dilawar was never charged with any crime and was never shown to have any connection with al-Qaida or the Taliban. But he was deprived of sleep, suspended by his wrists, kicked and kneed in the legs until he could no longer stand.
The film includes remarkably frank interviews with American servicemen, some of whom faced courts-martial in connection with Dilawar's death; with a fellow prisoner at Bagram; and with Carlotta Gall and Tim Golden, who reported Dilawar's story for The New York Times.
"Taxi to the Dark Side," however, does not simply recount a single, awful anecdote from the early days of the war on terror. Rather, it traces the spread of a central tactic in that war.
Gibney's argument is that what happened to Dilawar was not anomalous, but rather represented an early instance of what would soon be a widespread policy.
From Bagram in 2002, "Taxi to the Dark Side" charts a path to Guantánamo Bay and Abu Ghraib. It insists that the brutal treatment of prisoners in those places was hardly the work of a few "bad apples," as Pentagon officials said.
Instead, the sexual humiliation, waterboarding and other well-documented practices were methods sanctioned at the very top of the chain of command.
Though Gibney's own views are evident, he allows those who defend the use of torture on legal and strategic grounds to have their say.
By now, surely, the empty semantic debate about the word torture has been settled. But it is still important to recall that in the months after the Sept. 11 attacks, many were willing to consider the necessity of previously taboo tactics.
It was Vice President Dick Cheney who noted in a television interview that the fight against Islamic extremism would necessitate a trip to "the dark side."
"Taxi to the Dark Side" includes an interview with the former Justice Department official John Yoo and clips of former Defense Secretary Donald Rumsfeld and former Attorney General Alberto Gonzales responding to their critics.
And its essential fair-mindedness (which is not the same as neutrality) strengthens the film's accounting of the consequences, both strategic and moral.
Jack Clooney, a longtime FBI interrogator, argues that kindness can be a more effective way to manipulate a prisoner and gain information than cruelty. But young men who worked at Bagram and Abu Ghraib testify to the atmosphere of sadism in those places.
The film is long, detailed and not always easy to watch.
But sooner or later, we will need to understand what has happened in this country in the last seven years, and this documentary will be essential to that effort.