This month marks 20 years since al-Qaeda was founded in the Pakistani border city of Peshawar by Osama bin Laden and a handful of veterans of the war against the Soviets in Afghanistan, and the group is more famous and feared than ever. But its grand project – to transform the Muslim world into a militant Islamist caliphate – has been, by any measure, a resounding failure.

That's largely because Mr. bin Laden's strategy for arriving at this promised land is a fantasy. Al-Qaeda's leader prides himself on being a big-think strategist – but for all his brains, leadership skills and charisma, his overall strategy is self-defeating.

Mr. bin Laden's main goal is to bring about regime change in the Middle East and to replace the governments in Cairo and Riyadh with Taliban-style theocracies. He believes the way to accomplish this is to attack the "far enemy" (the United States), then watch as the supposedly impious, U.S.-backed Muslim regimes he calls the "near enemy" crumble.

This might have worked had the United States turned out to be a paper tiger that could sustain only a few blows from al-Qaeda. But it didn't. Mr. bin Laden's analysis showed no understanding of the vital interests – oil, Israel and regional stability – that undergird U.S. engagement in the Middle East, let alone the intensity of American outrage that would follow the first direct attack on the continental United States since the British burned the White House in 1814.

In fact, Mr. bin Laden's plan resulted in the direct opposite of a U.S. withdrawal from the Middle East. The United States now occupies Iraq, and NATO soldiers patrol the streets of Kandahar, the old de facto capital of Mr. bin Laden's Taliban allies. Relations between the United States and most authoritarian Arab regimes are stronger than ever.

For most leaders, such a complete strategic failure would require a rethinking. Not for Mr. bin Laden. He continues to conceive of the United States as his main foe. And al-Qaeda has fatally undermined its claim to be the true representative of all Muslims by killing thousands of them since Sept. 11, 2001. These two strategic blunders are the key reasons why al-Qaeda will ultimately lose.

But don't expect that defeat any time soon. For now, al-Qaeda continues to gather strength, both as a terrorist/insurgent organization based along the Afghan-Pakistani border and as an ongoing model for violent Islamists around the globe.

So how strong – or weak – is al-Qaeda at 20?

Earlier this year, a furious debate erupted in Washington between two influential counterterrorism analysts. Former CIA case officer Marc Sageman says the threat from al-Qaeda's core organization is largely over and warns that future attacks will come from the foot soldiers of a "leaderless jihad" – homegrown radicals with no formal connection to Mr. bin Laden's cadre.

On the other side stands Georgetown University professor Bruce Hoffman, who warns that al-Qaeda is on the march, not on the run.

Dr. Sageman's view of the leaderless threat is largely shared by key counterterrorism officials in Europe, who told me they can find no evidence of al-Qaeda operations in their countries. But top counterterrorism officials in the United Kingdom and the United States disagree. A 2007 U.S. National Intelligence Estimate concluded that al-Qaeda was growing more dangerous, not less.

Why the starkly differing views? Largely because U.S. and British officials are contending with an alarming new phenomenon, the deadly nexus developing between some militant British Muslims and al-Qaeda's new headquarters in Pakistan's lawless borderlands.

The lesson of several unnerving plots uncovered in the United Kingdom in the past few years is that the bottom-up radicalization described by Dr. Sageman becomes really lethal only when the homegrown wannabes manage to make contact with al-Qaeda Central in Pakistan.

"Hotheads in a coffeehouse are a dime a dozen," said Michael Sheehan, who until 2006 was the deputy New York police commissioner responsible for counterterrorism. "Al-Qaeda Central is often the critical element in turning the hotheads into an actual capable cell." Which is why it's so worrisome that counterterrorism officials have noticed dozens of Europeans making their way to tribal areas of Pakistan in the past couple of years.

And Mr. bin Laden's influence extends well beyond the Afghanistan-Pakistan theater. The same mainland European officials who are relieved not to be finding al-Qaeda Central cells in their countries now worry that Mr. bin Laden's North African ally, al-Qaeda in the Islamic Maghreb, may be finding recruits among poorly integrated North African immigrants living in France, Belgium, Spain and Italy.

Al-Qaeda's war for hearts and minds goes on, too. Mr. bin Laden once observed that 90 percent of his battle is waged in the media – and here, above all, he remains both relevant and cutting-edge. The most reliable guide to what al-Qaeda and the wider jihadist movement will do have long been Mr. bin Laden's public statements.

However, I think it highly unlikely that the group will be able to attack inside the United States in the next five years.

In the past, al-Qaeda terrorists trying to strike the U.S. homeland have had to slip inside from elsewhere, as the 9/11 hijackers did. No successful past plot has relied on al-Qaeda "sleeper cells" here, and there is little evidence that such cells exist today. Moreover, the United States is a much harder target than it was before 9/11. The U.S. government is on alert, as are ordinary citizens.

Homegrown terrorists might carry out a small-bore attack inside the United States, although the U.S. Muslim community, which is far better integrated than its European counterparts, has produced few violent radicals. And al-Qaeda itself remains quite capable of attacking a wide range of U.S. interests overseas. But on balance, we have less to fear from al-Qaeda now than we did in 2001.

We would be far better off if we managed to kill or capture al-Qaeda's innovative chief. But the U.S.-led hunt for Mr. bin Laden is turning up nothing. Washington hasn't had a solid lead on him since radio intercepts placed him at the battle of Tora Bora in eastern Afghanistan in December 2001. U.S. intelligence officials widely assume that he is now in or near Pakistan's tribal areas.

No matter Mr. bin Laden's fate, Muslims around the world are increasingly taking a dim view of his group and its suicide operations. In the late 1990s, Mr. bin Laden was a folk hero to many Muslims. But since 2003, as al-Qaeda and its affiliates have killed Muslim civilians by the thousands, support for Mr. bin Laden has nose-dived, according to Pew polls taken in key Muslim countries such as Indonesia and Pakistan.

At 20, al-Qaeda is losing its war, but its influence will live on. As Michael Scheuer, who founded the CIA's bin Laden unit in 1996, points out, "Their mission is accomplished: worldwide instigation and inspiration." To our grief, that legacy will endure, even after al-Qaeda is defeated.