For me, 9/11 will always dawn bright, still and routine, and end in confusion, anger and strange anticipation. The ugly gash was also a dividing line. Those of us in government were suddenly given a vague, intimidating sense of purpose. Events ahead, for good or ill, would gather into history.

The Sept. 11 anniversary now involves reflections on the nature of tolerance, on the fragility of national unity, on the selectivity of historical memory. At the time, however, the events of Sept. 11 were primarily a national security crisis. An enemy, with minimal expenditure, had taken thousands of lives, overturned a long-standing expectation of safety and disrupted a continental economy. Given advances in technology, future attacks could be worse.

In a series of speeches and documents (some of which I helped to write), President George W. Bush set out the elements of a strategic response. At West Point, he talked of preempting gathering threats. The military “must be ready to strike at a moment’s notice in any dark corner of the world.” In his 2002 State of the Union address, Bush argued that the rule of law, respect for women, equal justice and religious tolerance — the “non-negotiable demands of human dignity” — would be the basis for reform in Arab nations. In the National Security Strategy of 2002, Bush placed international development at the center of the response to terrorism: “Poverty, weak institutions and corruption can make weak states vulnerable to terrorist networks and drug cartels within their borders.”

These priorities became collectively known as the Bush Doctrine. Following initial failures in Iraq, critics argued that the doctrine was “in shambles.” Foreign policy “realists,” skeptical of preemption and democratic idealism, dismissed the five years after Sept. 11 as a brief, neoconservative interregnum.

Yet, a decade beyond Sept. 11, the Bush Doctrine has been adopted by the Obama administration and vindicated by events.

Iraq did illustrate the daunting difficulties of counterinsurgency and nation-building. But it did not discredit preemption. The American military and intelligence community remain in constant, kinetic motion. Under the direction of the president, thousands of Predator and Reaper unmanned aircraft conduct targeted killings in Afghanistan, Yemen, Somalia and Pakistan. Special Operations forces are prepared, as Osama bin Laden found, to strike without warning. Critics complain of a permanent, covert war. But President Obama has embraced this twilight struggle, the military is proud of its lethal effectiveness, and Americans are generally relieved and supportive. It is now a dangerous thing to be a sworn enemy of America.

After an extended Arab Spring, the realist practice of supporting favorable autocrats in the Middle East and North Africa seems hopelessly naive. The combined dictatorial rule of 95 years in Tunisia, Egypt and Libya collapsed in the course of eight months, and there is no reason to believe the revolution has ended. Citizen participation always carries the risk of poor choices by citizens. But it is now clear that autocratic and economically backward nations are inherently unstable, and that democratic transitions are the best hope of constructively channeling discontent. Obama has been a reluctant, foot-dragging convert to the democracy agenda. But he is a convert nonetheless.

Criticism of the Bush Doctrine was always based on a distortion — that it was somehow generated by neoconservative ideology. But Bush did not come out of a neoconservative foreign policy tradition. Each element of the doctrine was a response to concrete historical circumstances — the need to protect Americans from violence, the dangerous instability of the Middle East, the imperative of countering hatred with hope. Bush was not an ideological radical, just as Obama is not an ideological turncoat. Any president will be forced by duty to adopt similar views.

During the past decade, it is the foreign policy realists who ­haven’t come off particularly well. In the war on terrorism, they have often seemed satisfied during reverses, dismissive of progress and silent in American success. They play down the terrorist threat as “exaggerated” while enjoying the protection of the brave. They placed their bet in favor of permanent serfdom in the Middle East and now seem disappointed by historical miracles.

On Sept. 12, 2001, I entered the White House complex through blocks of eerily deserted streets, under cover of jets and helicopters. “We have expanded the security perimeter,” I was told by a guard. Since those days, America has expanded its security perimeter beyond Constitution Avenue to rural Yemen and Abbottabad, Pakistan. That is the admirable achievement of two presidents — preventing America from becoming a battlefield once again.