Two weeks ago, not far from here, bells tolled at Ground Zero. We commemorated the sixth anniversary of the September 11th attacks. And we marked the passage of another year without a terrorist attack on American soil. It is important to pause and reflect on how we reached this milestone, so that we can better understand what we must do to reach another one. This task grows more complicated with every passing year. In the wake of the September 11th attacks, the focus of the nation was crystallized. Our objective was clear: We knew who, and where, our enemies were,...