In an interview with Martha MacCallum, one of the co-chairmen of the 9/11 Commission said he believes the ISIS terror army "snuck up on" the United States.

Lee Hamilton's fellow chairman, Tom Kean, said recently that ISIS represents the first time since 9/11 that terrorists have "a state" where they could possibly train for and plot large-scale attacks on the U.S.

Hamilton was asked this morning whether the emergence of ISIS in Syria and Iraq has come as a surprise.

He noted the "enormous turmoil" in the Middle East overall, with U.S. interests being involved in each area.

"You have an intelligence community in the United States with enormous capabilities, very highly professional. But they can't focus on everything all the time. It's undoubtedly the fact that ISIS kind of snuck up on us in a way and became a much more powerful actor in that region of the world than we had previously thought," he said, adding that the U.S. did not "keep its finger" on ISIS.

Hamilton pushed back on those who have argued that more support to the Free Syrian Army could have kept ISIS in check.

"It's an easy thing to say, 'well if we arm the rebels, we could have solved this problem or been much farther down the road.' It's by no means clear that that's the case," said Hamilton.

Watch his full interview above, including his thoughts on the country's ability to prevent ISIS terrorists - who may have U.S. passports in some cases - from getting back into the U.S.