In yet another example of “blowback” actually undermining Islamist terrorism, the Mumbai mayhem may boost George W. Bush’s historical legacy. In the waning days of his presidency, the massacres highlighted one of Bush’s most significant but elusive achievements. Perhaps his greatest accomplishment is a non-event. After September 11, most Americans assumed they would endure a wave of terrorist attacks. Even those Americans who hate Bush must grant him at least some credit for the fact that not one major attack has occurred again on American soil.

Subsequent atrocities in London, Madrid, Bali, Jerusalem, and now Mumbai – among many others – as well as occasional warnings and arrests within the United States -- suggest that the terrorists kept trying. In assessing a president’s legacy, it is hard to celebrate something that did not happen. It is hard to build a monument or even to write clearly regarding a threat that, while palpable and potentially lethal, never materialized. The Bush Administration cannot of course divulge details of most operations it thwarted. Still, the fact that so far the United States has avoided another 9/11 demonstrates that many of the Bush Administration’s anti-terror strategies worked.

A similar challenge faces Cold War historians. How do we explain the decades-long record of relative peace with the Soviet Union, despite repeated fears not just of confrontation but of nuclear confrontation? In analyzing this bell that did not ring, we assess the fears of Armageddon to see whether they were reasonable or exaggerated. We try to understand how the Soviets acted and reacted at the time. And we examine the American policies to see what worked and what failed.

This mystery of how we avoided the worst case scenario so many expected explains the enduring fascination with the Cuban Missile Crisis. The “Thirteen Days” in October 1962 continue to attract so much attention because we came so close to war – and because we can study the actors on both sides. Especially since the Soviet Union fell, scholars and retired policy makers have done an impressive job reconstructing and deconstructing the excruciating chess game that ended in a Soviet retreat rather than worldwide apocalypse. In some ways now we can appreciate how close the world came to the brink, and salute both John Kennedy’s and Nikita Khruschev’s moderation in determining the happy outcome.

Of course, the no-new-9/11s debate is shrouded in much more mystery. In addition to the Bush administration’s admirable reluctance to violate national security to score some PR points, the Islamist terrorists’ chaotic, secretive world remains obscured too. Still, it seems clear that the Treasury’s crackdown on the flow of funds into and out of the United States helped inhibit the terrorists. Similarly, the greater scrutiny in general, the tightened security at airports and other vulnerable targets, and the immigration crackdowns have helped.

More controversial, of course, is the Patriot Act and other moves that came at a higher cost, namely America’s tradition of maximizing individual civil liberties. Those difficult questions enter the realm of political theology. Given the fog around the facts, that debate more reflects individuals’ commitments to civil liberties balanced against their faith in the judgment of Bush and the broader national security apparatus. The arrogance, incompetence, arbitrariness, characterizing so much of the Bush Administration has undermined its credibility on this critical issue, where it may have achieved some great successes.

The terrorist attacks in India were equally mistimed regarding Bush’s successor. President-elect Barack Obama’s decisions to keep on Bush’s Secretary of Defense Robert Gates and to appoint Hillary Rodham Clinton as Secretary of State partially reflect Obama’s own realization of the seriousness of the terrorist threat. As a New York senator when the Twin Towers fell, as a mother who first did not know exactly where in Manhattan her daughter was on September 11, Senator Clinton has a heartfelt, sophisticated disgust for Islamist terrorism. Moreover, al Qaeda’s recent videotape using an ugly racial epithet to characterize Barack Obama as servile, may have been ignored by much of the media, but could not have escaped Obama’s attention. The combination, during a presidential transition, of a revolting display of Islamist racism and a horrific explosion of Islamist terrorism, proves that this ugliness persists – and that a reprehensible ideology unites these murderers who target Westerners and democrats wherever possible.

Despite all the hype during a presidential campaign about a candidate’s skills, judgment, character, experience, and potential, external events often define presidencies. George W. Bush himself entered office expecting to focus on domestic affairs. The horrific murders in Mumbai – along with the continuing economic roller coaster – illustrate that Obama’s legacy, like that all of his predecessors, remains in the hands of powerful actors and historical forces beyond his control, no matter how talented he is, no matter how focused on this one leader we remain.