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In the light of several incidents or alleged plots that have been in the news in recent months -- the Fort Hood shootings and the break-up of a terrorist ring in Colorado -- it is appropriate to be re-examine the terrorist threat to the U.S. homeland, and how the debate over troop levels in Afghanistan might affect it.

The most important patterns in international terrorism, with particular reference to threats to the U.S. homeland, in the eight years since the 9/11 attacks can be summarized in two trends pointing in different directions. The first is that the group that accomplished 9/11, al Qaeda, is -- although still a threat -- less capable of pulling off something of that magnitude than it was in 2001. This is possible in large part because of a variety of measures...