On September 11, 2006, the fifth anniversary of Al Qaeda's attacks on America, another devastating terrorist plot was meant to unfold. Radical Islamists had set in motion a conspiracy to hijack seven passenger planes departing from Heathrow Airport, in London, and blow them up in midair. "Courting Disaster" (Regnery; $29.95), by Marc A. Thiessen, a former speechwriter in the Bush Administration, begins by imagining the horror that would have resulted had the plot succeeded. He conjures fifteen hundred dead airline passengers, televised "images of debris floating in the ocean," and gleeful jihadis issuing fresh threats: "We will rain upon you such terror and destruction that you will never know peace."

The plot, of course, was thwarted-an outcome that has been credited to smart detective work. But Thiessen writes that there is a more important reason that his dreadful scenario never came to pass: the Central Intelligence Agency provided the United Kingdom with pivotal intelligence, using "enhanced interrogation techniques" approved by the Bush Administration. According to Thiessen, British authorities were given crucial assistance by a detainee at Guantánamo Bay who spoke of "plans for the use of liquid explosive," which can easily be made with products bought at beauty shops. Thiessen also claims that Khalid Sheikh Mohammed, the primary architect of the 9/11 attacks, divulged key intelligence after being waterboarded by the C.I.A. a hundred and eighty-three times. Mohammed spoke about a 1995 plot, based in the Philippines, to blow up planes with liquid explosives. Thiessen writes that, in early 2006, "an observant C.I.A. officer" informed "skeptical" British authorities that radicals under surveillance in England appeared to be pursuing a similar scheme.

Thiessen's book, whose subtitle is "How the C.I.A. Kept America Safe and How Barack Obama Is Inviting the Next Attack," offers a relentless defense of the Bush Administration's interrogation policies, which, according to many critics, sanctioned torture and yielded no appreciable intelligence benefit. In addition, Thiessen attacks the Obama Administration for having banned techniques such as waterboarding. "Americans could die as a result," he writes.

Yet Thiessen is better at conveying fear than at relaying the facts. His account of the foiled Heathrow plot, for example, is "completely and utterly wrong," according to Peter Clarke, who was the head of Scotland Yard's anti-terrorism branch in 2006. "The deduction that what was being planned was an attack against airliners was entirely based upon intelligence gathered in the U.K.," Clarke said, adding that Thiessen's "version of events is simply not recognized by those who were intimately involved in the airlines investigation in 2006." Nor did Scotland Yard need to be told about the perils of terrorists using liquid explosives. The bombers who attacked London's public-transportation system in 2005, Clarke pointed out, "used exactly the same materials."

Thiessen's claim about Khalid Sheikh Mohammed looks equally shaky. The Bush interrogation program hardly discovered the Philippine airlines plot: in 1995, police in Manila stopped it from proceeding and, later, confiscated a computer filled with incriminating details. By 2003, when Mohammed was detained, hundreds of news reports about the plot had been published. If Mohammed provided the C.I.A. with critical new clues-details unknown to the Philippine police, or anyone else-Thiessen doesn't supply the evidence.

Peter Bergen, a terrorism expert who is writing a history of the Bush Administration's "war on terror," told me that the Heathrow plot "was disrupted by a combination of British intelligence, Pakistani intelligence, and Scotland Yard." He noted that authorities in London had "literally wired the suspects' bomb factory for sound and video." It was "a classic law-enforcement and intelligence success," Bergen said, and "had nothing to do with waterboarding or with Guantánamo detainees."

"Courting Disaster" was published soon after a terrorism scare-the attempt by Umar Farouk Abdulmutallab, an alleged affiliate of Al Qaeda, to blow up a Detroit-bound jet on Christmas Day-and the book has attracted a wide readership, becoming a Times best-seller. Recently, Thiessen was hired by the Washington Post as an online columnist. Neither a journalist nor a terrorism expert, he got his start as a publicist for conservative politicians, among them Jesse Helms, the late Republican senator from North Carolina. After Bush's election in 2000, he began writing speeches for Defense Secretary Donald Rumsfeld and, eventually, became a speechwriter in the Bush White House.

In his book, Thiessen explains that he got a rare glimpse of the C.I.A.'s secret interrogation program when, in 2006, he helped write a speech for President George W. Bush that acknowledged the program's existence and offered a spirited defense of it. "This program has given us information that has saved innocent lives," Bush declared. (My own history of the Bush Administration's interrogation policies, "The Dark Side," mentions this speech, and says that it supplanted a different version, prepared by Administration officials who disapproved of the interrogation program; Thiessen, in his book, disputes my reporting, insisting that although "many edits" were suggested by critics of abusive tactics, there was "no rival draft.") In an effort to bolster the President's speech, the C.I.A. arranged for Thiessen to see classified documents, and invited him to meet agency interrogators. He says that he emerged convinced of the program's merit. While researching his book, he was granted extensive interviews with several of the program's key architects and implementers, including Vice-President Dick Cheney; Michael McConnell, the former director of national intelligence; and Michael V. Hayden, the former C.I.A. director. The book, whose cover features a blurb from Cheney, has become the unofficial Bible of torture apologists.

"Courting Disaster" has a scholarly feel, and hundreds of footnotes, but it is based on a series of slipshod premises. Thiessen, citing McConnell, claims that before the C.I.A. began interrogating detainees the U.S. knew "virtually nothing" about Al Qaeda. But McConnell was not in the government in the years immediately before 9/11. He retired as the director of the National Security Agency in 1996, and did not rejoin the government until 2007. Evidently, he missed a few developments during his time in the private sector, such as the C.I.A.'s founding, in 1996, of its bin Laden unit-the only unit devoted to a single figure. There was also bin Laden's declaration of war on America, in 1996, and his 1998 indictment in New York, after Al Qaeda's bombing of two U.S. embassies in East Africa. The subsequent federal trial of the bombing suspects, in New York, produced thousands of pages of documents exposing the internal workings of Al Qaeda. A state's witness at the trial, a former Al Qaeda member named Jamal al-Fadl, supplied the F.B.I. with invaluable information about the group, including its attempts to obtain nuclear weapons. (Fadl did so without any coercion other than the hope of a future plea bargain. Indeed, the F.B.I., without using violence, has persuaded dozens of other suspected terrorists to coöperate, including, most recently, the Christmas Day bomber.)

In order to make the case that America was blind to the threat of Al Qaeda in the days before 9/11, Thiessen skips over the scandalous amount of intelligence that reached the Bush White House before the attacks. In February, 2001, the C.I.A.'s director, George Tenet, called Al Qaeda "the most immediate and serious threat" to the country. Richard Clarke, then the country's counterterrorism chief, tried without success to get Condoleezza Rice, Bush's national-security adviser, to hold a Cabinet-level meeting on Al Qaeda. Thomas Pickard, then the F.B.I.'s acting director, has testified that Attorney General John Ashcroft told him that he wanted to hear no more about Al Qaeda. On August 6, 2001, Bush did nothing in response to a briefing entitled "Bin Laden Determined to Strike in the U.S." As Tenet later put it, "The system was blinking red."

Thiessen presents the C.I.A. interrogation program as an unqualified success. "In the decade before the C.I.A. began interrogating captured terrorists, Al Qaeda launched repeated attacks against America," he writes. "In the eight years since the C.I.A. began interrogating captured terrorists, Al Qaeda has not succeeded in launching one single attack on the homeland or American interests abroad." This is not exactly a textbook demonstration of causality. Moreover, the claim that American interests have been invulnerable since the C.I.A. began waterboarding is manifestly untrue. Al Qaeda has launched numerous attacks against U.S. targets abroad since 9/11, including the 2004 attack on the Hilton Hotel in Taba, Egypt; the 2003 and 2009 attacks on hotels in Indonesia; four attacks on the U.S. Consulate in Karachi; and the assassination of Lawrence Foley, a U.S. diplomat, in Jordan. In 2007, Al Qaeda attacked Bagram Air Base, in Afghanistan, killing two Americans and twenty-one others, in a failed attempt to assassinate Cheney, who was visiting. Indeed, Al Qaeda's relentless campaign in Afghanistan has helped bring about the near-collapse of U.S. policy there. In Iraq, the Al Qaeda faction led by Abu Musab al-Zarqawi killed hundreds of U.S. soldiers.

Terrorism experts have advanced many reasons that Al Qaeda has not managed a successful attack inside the U.S. since 9/11. For one thing, Peter Bergen suggests, America, in addition to improving its security procedures, "has spent hundreds of billions of dollars on improving intelligence." This effort has involved better coördination between the C.I.A., the F.B.I., and the international community, as well as tightened surveillance.

Thiessen's impulse, however, is to credit C.I.A. interrogators at every turn. He portrays the agency's coercive handling, in 2002, of Abu Zubaydah-he was subjected to beatings, sexual humiliation, temperature extremes, and waterboarding, among other techniques-as another coup that saved American lives. Information given by Zubaydah, Thiessen writes, led to the arrest, two months later, in Chicago, of Jose Padilla, the American-born Al Qaeda recruit. But Ali Soufan, a former F.B.I. agent, has testified before Congress that he elicited Padilla's identity from Zubaydah in April, 2002-months before the C.I.A. began using its most controversial methods. Soufan, speaking to Newsweek, said of Zubaydah's treatment, "We didn't have to do any of this." Philip Zelikow, the former executive director of the 9/11 Commission, has described Soufan as "one of the most impressive intelligence agents-from any agency." Thiessen dismisses Soufan's firsthand account as "simply false," on the ground that another F.B.I. agent involved in Zubaydah's interrogation-whom Thiessen doesn't identify-told the Justice Department's inspector general that he didn't recall Soufan's getting the information.

Thiessen, citing the classified evidence that he was privileged to see, claims that opponents of brutal interrogations can't appreciate their efficacy. "The assessment of virtually everyone who examined the classified evidence," he writes, is that the C.I.A.'s methods were justified. In fact, many independent experts who have top security clearances, and who have had access to the C.I.A.'s records, have denounced the agency's tactics. Among the critics are Robert Mueller, the director of the F.B.I., and four chairmen of the Senate Intelligence Committee. Last year, President Obama asked Michael Hayden, the C.I.A. director, to give a classified briefing on the program to three intelligence experts: Chuck Hagel, the former Republican senator from Nebraska; Jeffrey Smith, a former general counsel to the C.I.A.; and David Boren, the retired Democratic senator from Oklahoma. The three men were left unswayed. Boren has said that, after the briefing, he "wanted to take a bath." In an e-mail to me, he wrote, "I left the briefing by General Hayden completely unconvinced that the use of torture is an effective means of interrogation. . . . Those who are being tortured will say anything."

Tellingly, Thiessen does not address the many false confessions given by detainees under torturous pressure, some of which have led the U.S. tragically astray. Nowhere in this book, for instance, does the name Ibn Sheikh al-Libi appear. In 2002, the C.I.A., under an expanded policy of extraordinary rendition, turned Libi over to Egypt to be brutalized. Under duress, Libi falsely linked Al Qaeda and Saddam Hussein's alleged biochemical-weapons program, in Iraq. In February, 2003, former Secretary of State Colin Powell gave an influential speech in which he made the case for going to war against Iraq and prominently cited this evidence.

Thiessen never questions the wisdom of relying on C.I.A. officials to assess the legality and effectiveness of their own controversial program. Yet many people at the agency aren't just worried about the judgment of history; they're worried about facing prosecution. As a report by the Justice Department's Office of Professional Responsibility notes, the agency has a "demonstrated interest in shielding its interrogators from legal jeopardy."

"Courting Disaster" downplays the C.I.A.'s brutality under the Bush Administration to the point of falsification. Thiessen argues that "the C.I.A. interrogation program did not inflict torture by any reasonable standard," and that there was "only one single case" in which "inhumane" techniques were used. That case, he writes, involved the detainee Abd al-Rahim Nashiri, whom a C.I.A. interrogator threatened with a handgun to the head, and with an electric drill. He claims that no detainee "deaths in custody took place in the C.I.A. interrogation program," failing to mention the case of a detainee who was left to freeze to death at a C.I.A.-run prison in Afghanistan. Referring to the Abu Ghraib scandal, Thiessen writes that "what happened in those photos had nothing to do with C.I.A. interrogations, military interrogations, or interrogations of any sort." The statement is hard to square with the infamous photograph of Manadel al-Jamadi; his body was placed on ice after he died of asphyxiation during a C.I.A. interrogation at the prison. The homicide became so notorious that the C.I.A.'s inspector general, John Helgerson, forwarded the case to the Justice Department for potential criminal prosecution. Thiessen simply ignores the incident.

Thiessen also categorically states, "The well-documented fact is there was no torture at Guantánamo." One person who would disagree with this remark is Susan Crawford, the conservative Republican jurist whom Bush appointed to serve as the top "convening authority" on military commissions at Guantánamo. Last year, she told Bob Woodward, of the Washington Post, that there was at least one Guantánamo detainee whose prosecution she couldn't allow because his abuse "met the legal definition of torture."

Perhaps the most outlandish falsehood in "Courting Disaster" is Thiessen's portrayal of Obama and the Democrats as the sole opponents of brutal interrogation tactics. Thiessen presents the termination of the C.I.A. program as a renegade action by President Obama, who has "eliminated our nation's most important tool to prevent terrorists from striking America." Yet Thiessen knows that waterboarding and other human-rights abuses, such as dispatching prisoners into secret indefinite detention, were abandoned by the Bush Administration: he wrote the very speech announcing, in 2006, that the Administration was suspending their use.

In fact, the C.I.A.'s descent into torture was ended by an outpouring of opposition from critics inside and outside the Administration-including officials within the C.I.A., who registered their concerns with Helgerson. In 2004, Helgerson wrote a pointed confidential report questioning the legality, the medical safety, and the humaneness of the program, which spurred conservative, Bush-appointed lawyers in the Justice Department to withdraw arguments that had been made to justify the program. F.B.I. officials and military leaders, including the four-star General John Vessey, the former chairman of the Joint Chiefs of Staff, turned against the Bush Administration interrogation program. So did Senator John McCain; he later described waterboarding as torture. In 2006, the Supreme Court ruled that American officials had to treat Al Qaeda suspects humanely, or face charges of war crimes.

Thiessen's effort to rewrite the history of the C.I.A.'s interrogation program comes not long after a Presidential race in which both the Republican and the Democratic nominees agreed that state-sponsored cruelty had damaged and dishonored America. The publication of "Courting Disaster" suggests that Obama's avowed determination "to look forward, not back" has laid the recent past open to partisan reinterpretation. By holding no one accountable for past abuse, and by convening no commission on what did and didn't protect the country, President Obama has left the telling of this dark chapter in American history to those who most want to whitewash it.