As to new sanctuaries, there may arise new Afghanistans where would-be radicals can congregate and form lasting ties. Numerous jihads continue without letup. Chechnya remains a bloody standoff, attracting militant Islamists as well as homegrown radicals. Kashmir has died down but may soon re-ignite. Xinjiang remains turbulent, and Indonesia may flare up as well despite, or maybe because of the government's late-April crackdown on Jemaah Islamiyah and its military approach in Aceh.

An even more troubling phenomenon is the discovery of possible cells in the United States itself. In essence, the September 11 hijackers were infiltrators in the United States, taking advantage of permeable U.S. borders to plot their attacks. The arrests of alleged militants in Lackawanna, Seattle, Detroit, Chicago, Florida and Portland also indicate that Islamic radicalism is appealing to individuals rooted in American communities. The FBI estimates that several hundred militants linked to Al-Qaeda are in the United States. This challenge is distinct from protecting borders and ensuring proper visa issuance. But it is certainly no less daunting.

But Today the Struggle

THERE ARE few easy choices in the war against terrorism, and no silver bullets. Anti-U.S. sentiment will remain strong, and it may even grow as the United States aggressively disrupts existing militant networks. Conflicts in Chechnya, Kashmir and elsewhere will rise or decline largely on their own accord, with the United States having at best marginal influence. As a result, radicals will continue to enjoy success in recruiting and fundraising. Even if Al-Qaeda's current leadership cadre is killed or arrested, its ideals and legend will remain strong, inspiring the next generation of radicals--who may well manage to get hold of truly dangerous biological or radiological substances.

As a result, current operations against existing cadres remain necessary At times, killing the right leader may dishearten a movement or a cell, and his arrest may produce valuable information that can wrap up a much broader network. Such benefits, even if ephemeral, are worth the effort, and even if they may create problems over the long-term. This is because failure to act would not only allow current operations to succeed, but would also enable existing terrorist networks to deepen and expand, making attacks deadlier and more frequent.

There is no easy long-term strategy that guarantees success. Instead, the United States and its allies must accept the inevitability of a large, global movement bent on murder as a form of political expression. With skill and energy; we can beat it back. Outright defeat will be far harder. That may depend ultimately on the proverbial draining of the political swamp. But by any measure it is a very large swamp.

Daniel Byman is assistant professor in the Security Studies Program of Georgetown University and a non-resident senior fellow at thc Saban Center for Middle East Policy at the Brookings Institution