Not every Bush veteran agrees, of course. Marc Thiessen, a former White House speechwriter, has a new book called “Courting Disaster: How the C.I.A. Kept America Safe and How Barack Obama Is Inviting the Next Attack.” Tom Ridge, the former homeland security secretary, told me before the Christmas Day plot that under Obama, Washington had “lost a certain sense of urgency and commitment to combating terrorism.” Most disturbing to the Bush camp, even to those who generally see continuity in Obama’s policies, have been Attorney General Eric Holder’s decisions to release legal memos that described interrogation techniques used by the C.I.A., to reinvestigate allegations of interrogation abuse by C.I.A. officers and to take Khalid Shaikh Mohammed, the self-declared mastermind of the Sept. 11 attacks, to New York to face trial in civilian court. Hayden recalled warning Jim Jones, Obama’s national security adviser, last spring not to alienate the C.I.A. by dredging up the past. “You’re about to spend the next 46 months without a clandestine service,” Hayden recalled saying. “If these guys don’t think you have their back, they’re not going to be very adventurous.”

There is ample historical precedent for this cycle. During times of national crisis, Washington often claims more authority, sometimes to the point of excess, then slowly cedes it back, from the Sedition Act signed by John Adams to Abraham Lincoln’s suspension of habeas corpus during the Civil War to Franklin D. Roosevelt’s internment of Japanese-Americans during World War II — all cases in which the system eventually corrected itself in one fashion or another. “Historically the more we move away from a crisis, the better we’re able to see the costs and benefits of what we’re doing, and we go from being extremely risk-averse to finding a better balance,” says Geoffrey Stone, a professor and former dean at the University of Chicago law school.

Bush has pointed to another historical pattern. In private discussions with associates during the 2008 presidential campaign, he predicted that if a Democrat won, he or she would be like Dwight Eisenhower to his Harry Truman. Just as Eisenhower on the campaign trail criticized Truman’s policies in the early years of the cold war only to essentially adopt them after taking office, Bush anticipated that his successor would preserve most of what he had put in place. Of course, this conveniently fits into Bush’s hope that, like Truman, he will look better in the eyes of history. A senior Obama adviser scoffed at the idea that Bush advisers see continuity, arguing that they are trying to launder their reputations by claiming validation. But it is true that much of the Bush security architecture is almost certain to remain part of the national fabric for some time to come, thanks to Obama.

Stone, who helped bring Obama to the University of Chicago law school, says his former colleague must be wary of doing anything that would increase the risk of a terrorist attack against the United States. “He may feel in fact,” Stone says, “that it’s a more dangerous world than he thought it was, that some of these measures may be more necessary than he thought.”

STONE JOINED A GROUP of human-rights and civil-liberties advocates at the White House last spring for a meeting with Obama to talk about issues of interrogation and detention. Obama had struggled through a rocky few months trying to find the balance between security and liberty, arguing that America did not need to sacrifice one for the other.

The decision to close the Guantánamo prison sparked a revolt in Congress, even among Democrats who worried about suspected terrorists being transferred to prisons in their states. And while the administration has selected an Illinois facility to house some of the detainees, the Jan. 22 deadline to close Guantánamo will not be met. An attempt to release into the United States 17 Chinese Uighurs who were deemed no threat to Americans collapsed. And although Obama authorized the release of memos detailing the use of waterboarding and other techniques now banned, he refused to release photographs showing abuse of detainees.

For Brennan, these issues were a chance to get right what he thought went wrong under Bush. But he has found himself at odds with other advisers at times. When Craig and Holder wanted to release the memos about C.I.A. interrogation methods, Brennan initially agreed, reasoning that the tactics in the memos had by then been banned. But he later reversed himself and sided with the C.I.A., which argued that the memos would give terrorists too much information about how American interrogators work. Brennan likewise stood with Gates and military leaders who argued unsuccessfully that releasing photographs of the abuses would inflame radicals and endanger American troops. Gen. Ray Odierno, the top commander in Iraq, made a personal appeal to Obama during a visit to Washington, and the president agreed to reject Craig’s recommendation to release the photos. Brennan also found an ally at times in Rahm Emanuel, who was said to think that the politics of these decisions were being mishandled and that fights over detention policy used up political capital better spent on priorities like health care and the economy.