The nature and threat of radical Islamic terrorism has been altered and expanded by ISIS, and Al-Qaeda has been quietly rebuilding its capabilities in preparation for ISIS’ defeat on the battlefield, according to terrorism officials.

Three renowned experts on terrorism testified before the House Armed Services Committee on Tuesday, giving detailed briefs on their assessments of the current terrorist threat, and possible actions the U.S. could take as it continues its counterterrorism efforts.

Bruce Hoffman from the Center for Security Studies at Georgetown, Brian Michael Jenkins from the RAND Corporation, and former Green Beret Michael Sheehan from West Point’s Combating Terrorism Center spoke to the challenges military and intelligence services will continue to face, specifically with regard to a resurgent Al-Qaeda and the incredibly complex security situation that will occur once ISIS is driven from its territorial strongholds.

According to Hoffman, the war in Syria has brought over 40,000 foreign fighters from over 100 different countries, given them combat experience and training, and nurtured radicalization. These numbers are far higher than all estimates for the famed mujahedeen of the Soviet-Afghan war, who went on to form terrorist networks and insurgencies worldwide capable of executing major attacks.

Despite a formal split from ISIS in 2014, Ayman al-Zawahiri—the quiet AQ number two since the Bin Laden days who now runs the network—is preparing to absorb some of the ISIS leadership he originally cast out. By sending AQ’s most experienced commander Saif al-Adl to Syria in 2015, al-Zawahiri is ready to exploit the potential vacuum of leadership and organization that will result from ISIS losses.

While all three experts agreed that ISIS represents an especially dangerous threat, one that will last for years to come, it is not an existential one for the United States. However, the relative success seen in stopping attacks inside the United States has been the result of unprecedented focus on law enforcement and security measures enacted after 9/11.

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Europe will likely continue to see spectacular attacks due to the refugee crisis. Law enforcement and intelligence services there are overwhelmed and unable to effectively screen for security threats from the sheer volume of immigrants. By limiting the numbers of migrants, and subjecting them to increased scrutiny, the U.S. has so far avoided lapses in security that would allow a major attack from terrorists exploiting the immigration situation.

Ultimately, none of them had conclusive answers for a U.S. strategy going forward, conceding only that there are no easy answers, and that disengagement from contingency operations overseas will not be an effective strategy.

Image courtesy of the BBC