Written by Scott Stewart
Extremist movements rise and fall, but the key, high-impact threats remain consistent. In my assessment, the most severe terrorist threat to targets in the United States today stems from professional terrorist cadres, such as the group of 19 attackers responsible for the 9/11 attacks.

However, due to security improvements made in the wake of the 9/11 attacks, extremist groups have had difficulty getting trained operatives into the United States…