"Abu Musab al-Suri is someone I got to know pretty well because he's a Syrian. Very bright guy, lived..." — Peter Bergen

The sitting prime minister, Jose Aznar, who had strongly backed the U.S.-led Iraq War, was unseated by a challenger who then pulled Spanish troops out of Iraq. The Madrid terrorist attacks are generally regarded as being the key to why Aznar, who had been leading in the polls, was defeated.

Trump has long said he favors a 'safe zone' in Syria to prevent Basher al Assad's regime from carrying out indiscriminate airstrikes against Syrian civilians and to halt the refugee flow out of Syria.

When Abu Zubaydah was shown a series of photos of al Qaeda members by Soufan, he identified one of them as the operational commander of 9/11, Khalid Sheikh Mohammed.

President-elect Donald Trump has a host of national security challenges to deal with as he assumes office, from the resurgence of the Taliban in Afghanistan to the grinding Syrian civil war to the flexing of Russian muscles under President Vladimir Putin to how to deal with ISIS as the terrorist army retreats in Iraq.