A comparative analysis of Islamic extremism post-9/11 to 2015 and the effectiveness of the counterterrorism (CT) authorities to counter it in both Western Europe and the United States was conducted. Four measures of effectiveness revealed that 2010–2015 saw a gradual increase in jihadi attacks and in casualties emanating from these attacks, and more jihadists, foreign fighters, and material supporters. Additionally, 2013–2015 saw a 22 percent reduction both in Western Europe and the U.S. CT agencies' ability to counter Islamic extremism. We are losing the War on Terror and our citizens are less safe than they were six years ago. Further analysis revealed that singleton jihadists: (1) were much harder than group-based jihadists to uncover, (2) have been increasing since 2009, and (3) have generated over 70 percent of all jihadi violence. Finally, numerous similarities exist between Western Europe and the United States with respect to jihadism in their homelands and their respective CT effectiveness, indicating close cross-Atlantic CT collaboration since 9/11. This in-depth analysis provides essential threat/hazard information to security, law enforcement, intelligence, and policymaking personnel and the greater homeland security communities.