Nine days after the Sept. 11, 2001, attacks, President George W. Bush stood before Congress to outline a two-pronged response to history’s deadliest terrorist act: dramatic improvements in security at home and an all-out assault on what he called a “fringe form of Islamic extremism” at war with the West.

Fifteen years later, the first goal arguably has been met, as Americans by almost every measure are safer today from another 9/11-scale attack than in 2001.

Yet the struggle to defeat the global network of violent, rabidly anti-Western jihadist groups has recorded fewer successes. Indeed, the problem appears to have grown bigger.

The al-Qaida organization once led by Osama bin Laden has been decimated and is no longer capable of orchestrating a sophisticated, trans-national plot on its own, terrorism experts say they believe. Al-Qaida’s branches in North Africa and Yemen also have been weakened by Western military strikes and ongoing fighting with rival factions.

But al-Qaida’s powerful and locally popular Syrian branch, Jabhat Fateh al-Sham, commands an army of thousands of trained fighters and now serves as a base for senior al-Qaida operatives experienced in making explosives and carrying out terrorist attacks, U.S. officials and terrorism experts say. The Syrian group recently announced it had split with al-Qaida, but U.S. officials say the claim is not credible.

Meanwhile, the Islamic State, despite military setbacks in Iraq and Syria, has demonstrated a growing capability to direct – or inspire – simple-but-lethal terrorist attacks around the world.

“The threat is actually worse: It has metastasized and spread geographically,” said Richard Clarke, a top terrorism adviser to three presidents and the man who famously warned the Bush administration about the growing risk from al-Qaida in the weeks before 9/11.

Both the Bush and Obama administrations thwarted multiple terrorist plots and achieved significant military successes against specific terrorist factions and key leaders, including al-Qaida in Iraq founder Abu Musab al-Zarqawi in 2006, bin Laden in 2011 and the Islamic State’s No. 2 commander, Abu Muhammad al-Adnani, who reportedly was killed in a U.S. airstrike last month.

Yet both administrations struggled to find a formula for blunting the appeal of violent jihadist groups or preventing thousands of young Muslims from enlisting in a global movement fueled by hatred and bent on destruction.

There is little to show for more than a decade’s worth of U.S.-sponsored programs aimed at countering extremist messages, terrorism experts say, and U.S. officials have struggled to block the jihadists’ use of social media or disrupt international funding and support for extreme interpretations of Islam. Meanwhile, U.S. policies, from the Iraq invasion in 2003 to the ongoing use of armed drones against suspected terrorists, have helped drive new recruits to al-Qaida and the Islamic State, former U.S. officials and analysts say.

“We generate more enemies than we are able to take out,” said former congresswoman Jane Harman, D-California, a chairwoman of the House Intelligence Committee in the years after 9/11, who now is president of the Woodrow Wilson International Center for Scholars. “Our military power remains extraordinary. But winning this fight requires projecting a narrative about American values and interests. And we have failed to do that.”

The National Counterterrorism Center (NCTC), which was created by the post-9/11 wave of intelligence reforms, mounted a series of efforts to map the radicalization paths of Islamist militants. But there are divided opinions on what came of that work.

Michael Leiter, who led the NCTC from 2007 to 2011, said the research produced important insights that have helped guide U.S. counterterrorism policy, but never led to the discovery of sequences or patterns that would reliably signal an individual’s intent to carry out an attack.

Soon after President Obama took office in 2009, the new administration’s security team began looking for novel approaches to countering radicalization.

A week after his inauguration, former officials said, Obama directed his national security advisers to draft a report summarizing the government’s efforts on countering violent extremism, identifying promising approaches.

“The president wanted a new strategy,” said a former senior administration official, who spoke on the condition of anonymity in discussing the administration’s internal deliberations.

The effort went nowhere, the former official said, in part because key advisers including John Brennan, Denis McDonough and Ben Rhodes could never agree on who should be in charge.

The administration’s focus became the escalating CIA drone campaign in Pakistan, and the half-hearted push on countering violent extremism “got dropped,” the former official said.

A hard-learned lesson of the last 15 years, current and former officials say, is that the most effective counter-radicalization messages can only come from Muslims themselves – religious leaders and institutions as well as governments, which must address the political and social disparities that fuel extremism.

But U.S. officials have been largely frustrated in their efforts to persuade Muslim allies to take more aggressive measures in their home countries.