Why are some conservatives so determined to let liberals off the hook for 9/11? For the past five years, leading pundits on the left have blamed American foreign policy for the blowback of Muslim rage that produced 9/11. In my book The Enemy at Home I turn the tables and say that it is liberal foreign policy and liberal values projected abroad that are largely responsible for this blowback.

In a recent column, Victor Davis Hanson charges that my argument puts me in the category of leftist author Susan Sontag and fundamentalist preacher Jerry Falwell. Sontag blamed 9/11 on “specific American alliances and actions.” Falwell said 9/11 was God’s punishment for America’s sins. Both seemed to imply that America deserved it.

But this is not what I say at all. My book asks a completely secular question: why did the guys who did 9/11 do it? Five years after this event, it’s not an unreasonable question. To ask it is not to “justify” the attacks any more than to ask whether British appeasement of Hitler prior to his invasion of Poland “justified” that invasion. Explanation is not the same as justification.

Of course Bin Laden and his co-conspirators bombed the World Trade Center and the Pentagon. But what put them in a position to do it? What gave them the courage to attack the world’s sole superpower? How has radical Islam been so successful in recruiting Muslims to its cause? Hanson offers no explanation, merely proclaiming Al Qaeda’s ideology “rambling” and “incoherent.” But consider three key questions.

First, without the Khomeini regime coming to power in Iran in 1979, would 9/11 have occurred? Radical Islam has been around since the 1920s, but for decades it was on the margins of power. Then in 1979 it captured a major state. Khomeini is the first Muslim leader to call America the Great Satan and to call for a worldwide revolution of Muslims committing martyrdom and jihad against the U.S. The Khomeini revolution paved the road to 9/11.

So how did we get Khomeini? When Jimmy Carter was elected in 1979 his liberal advisors told him that he could not consistently uphold human rights and support the Shah of Iran. Carter pulled the Persian rug out from under the Shah, and in trying to get rid of the bad guy, he got the worse guy. So here is a concrete way in which liberal foreign policy handed radical Islam control of its first major state.

Here’s a second question: Without the weakness and inaction of the Clinton administration during the mid-to-late 1990s, would 9/11 have happened? Recall that after the cold war the Islamic radicals went back to their home countries. They were fighting to overthrow their local governments, what they called the “near enemy.” Then they made a fateful decision to shift course and attack the “far enemy,” the United States.

Why? If you can’t defeat Mubarak in Egypt or the royal family in Saudi Arabia, what makes you think you can take on the world’s sole superpower? Bin Laden says he got the idea that America was weak and cowardly and could be attacked with impunity. So the radical Muslims launched a whole series of test strikes—from Khobar Towers to the bombing of U.S. embassies in East Africa to the suicide attack on the U.S.S. Cole—to test their theory of American weakness. And when in each case the Clinton administration failed to respond, or responded with pathetic ineffectiveness, this confirmed Bin Laden in his suspicion of American pusillanimity. By his own account Bin Laden says the radical Muslims were emboldened to conceive a grander strike, the one that we suffered on 9/11. Continued...