How long does it take a nation to forget a wound to its heart?

Six years ago, Islamic terrorists murdered 3000 Americans. The country watched in horror as men and women flung themselves from the top stories of the World Trade Center, desperately attempting to escape the flames rising beneath them; as firefighters were crushed beneath the falling towers; as Americans were consumed by a ball of fire springing from Flight 77 at the Pentagon; as Flight 93 plummeted to consecrated earth in Pennsylvania.

If we took one day to mourn each of the lives taken on September 11, our mourning period would last more than eight years. It has been just six years, and America is already in grave danger of wiping clean the slate of memory.

Did our acute need for closure overcome our more honorable instinct for justice? Were we so horrified by the images of September 11 that we deliberately blinded ourselves to the continuing presence of evil in our world, preferring to retreat to the pre-September 11 rut?

Or has a far more insidious tendency taken root in our politics?

September 11, common parlance has it, changed everything. "Tonight we are a country awakened to danger and called to defend freedom," President Bush told Americans on September 20, 2001. "Our grief has turned to anger, and anger to resolution. Freedom and fear are at war."

And for the first few years, Americans agreed with President Bush: Islamism was a global problem, not a simple law enforcement issue. Islamic tyranny, combined with a willingness to harbor and finance international terrorist groups, could not be tolerated. We would not wait for another 9/11 -- we would act firmly, decisively and pre-emptively.

But from the beginning, the poisonous seed of homegrown anti-Americanism was present. It was present in the crop of ridiculous 9/11 conspiracy theories supported by certain celebrities, academics and politicians. It was present in the immediate condemnation of military action in Afghanistan. It was present in the reflexive self-criticism of the extreme left, which suggested that 9/11 was the foreseeable result of xenophobic American foreign policy. And over time, that seed grew. As Americans grew weary of war without immediate victory and the long-term task of reshaping the Middle East, the seed sprouted into full flower. Now, on the sixth anniversary of the September 11 attacks, the most important ideological battle -- the battle to define America's aims and self-image -- is between those who see America as the perpetrator of racism and violence and those who see America as a force for good in the world. The ideological battle is the battle to define the lessons of 9/11. On one side stands the Vietnam-era left, which blames the United States (and in particular, its support for Israel) for the attacks of 9/11 and suggests that the American response to 9/11 demonstrated our boorish egocentrism and bigoted misinterpretation of world politics. On the other side stands the right, which sees Islamism, not American exceptionalism, as our true enemy. In the center, wavering, stands the bulk of the American people. The legacy of 9/11 remains in doubt. A century from now, 9/11 will be seen either as the death knell of a crumbling civilization or a rallying cry for a renewed, American-led movement for freedom. The choice remains in our hands.