The Homeland Security Department warned of a possible ISIS terrorist attack in the U.S. five days before today’s New York City subway bombing, noting that it would likely be a hard-to-prevent lone wolf assault.

“We assess there is currently an elevated threat of [homegrown] lone offender attacks by ISIS sympathizers, which is especially concerning because mobilized lone offenders present law enforcement with limited opportunities to detect and disrupt their plots,” according to Robin Taylor, acting deputy under secretary for intelligence operations at Homeland Security.

Taylor revealed the new warning during a Senate hearing last week during which he added that while ISIS and al Qaeda have been hobbled on the battlefield, they remain strong in social media and in recruiting U.S. sympathizers.

To the Senate Homeland Security and Governmental Affairs Committee chaired by Wisconsin Sen. Ron Johnson, Taylor said, “We continue to monitor the evolving threat posed by ISIS. ISIS fighters’ battlefield experience in Syria and Iraq have armed it with advanced capabilities that most terrorist groups do not have. Even as the so-called ‘caliphate’ collapses, ISIS fighters retain their toxic ideology and a will to fight. We remain concerned that foreign fighters from the U.S. or elsewhere who have traveled to Syria and Iraq and radicalized to violence will ultimately return to the U.S. or their home country to conduct attacks.”

He added that “core” al Qaeda “and its affiliates remain a major concern for DHS. Despite the deaths of many AQ senior leaders, the group and its affiliates maintain the intent, and, in some cases, the capability to facilitate and conduct attacks against U.S. citizens and facilities. The group and its affiliates have also demonstrated that capability to adjust tactics, techniques and procedures for targeting the West.”

Paul Bedard, the Washington Examiner's "Washington Secrets" columnist, can be contacted at pbedard@washingtonexaminer.com