Thomas Joscelyn, a senior fellow at the Foundation for Defense of Democracies:
— ISIS is an international organization with cells in many countries other than Iraq and Syria, so ISIS member travel to the West could come other countries as well. Indeed, according to European intelligence, most “fighters” who have gone to fight for the organization and returned home were citizens of said countries, making it easier for them to potentially hop a flight to the U.S. and plan attacks on Americans.
— ISIS is a very resilient organization and it is difficult if not impossible to know the organization’s real numbers.
— They are guerrilla warfare experts and have members capable of planning attacks on the West, and in fact are currently doing so.
— Al Qaida and other terrorist organizations are still a threat to the U.S.
— Europol is putting more intelligence assets into refugee hotspots — Italy, the Mediterranean, Greece — in order to determine who may pose a real terrorism threat; Eurozone counterterrorism elements are overwhelmed at the moment and are attempting to put resources where they will do the most good in spotting suspects before they act.
— U.S. leaks of European threat intelligence — such as that which occurred with the Manchester bombing — “did cause problems” and it needs to be “tamped down permanently.”
— The U.S. and allies are not doing enough to shut down online jihadist training via web sites and social media.
Robin Simcox, the Margaret Thatcher fellow at the Heritage Foundation:
— As U.S.- and Western-allied forces recapture ground lost to ISIS in Iraq and Syria, fighters are more likely to disperse; many will return to their homes in Europe, meaning they could also move on to other Western countries like the U.S.
— Americans traveling aboard are continually at risk of terrorist attacks from ISIS, Al Qaida and similar groups, particularly in Europe.
— Children of radicalized elements also pose a future threat.
— European countries are having trouble sending back illegal immigrations to their home countries who pose security threats because those governments won’t take them back.
Dr. Colin P. Clarke, political scientist at the RAND Corporation:
— Former ISIS fighters returning to their home countries may attempt to resurrect dormant networks, training new fighters, and begin new insurgencies.
— The U.S. must continue to put resources into preventing foreign terrorist fighters from entering the country, including physical border security, intelligence-sharing with allies, and intelligence and law-enforcement coordination.
— Good data on which counterterrorism programs are effective is largely absent, so much more research must be done in order to produce more effective policies.
— As the ISIS caliphate is dissipated, new challenges will arise for the West, and while the danger to the U.S. from this and other terrorist organizations is real, it is manageable.
— There is some credence to the belief that terrorists could use attempt to sneak into the U.S. via the Southwest border with Mexico — though there is likely no existing infrastructure within the U.S. “that would facilitate some kind of attack.”
— There is only a small percentage of current ISIS fighters who may attempt to return to the U.S., though they are the most-trained and most lethal.