The New York Times does us all a great favor with this retrospective on Afghanistan:
With a senior American diplomat, R. Nicholas Burns, leading the way, they thundered around the country in Black Hawk helicopters, with little fear for their safety. They strolled quiet streets in Kandahar and sipped tea with tribal leaders. At a briefing from the United States Central Command, they were told that the Taliban were now a “spent force.”
“Some of us were saying, ‘Not so fast,’ ” Mr. Burns, now the under secretary of state for political affairs, recalled. “While not a strategic threat, a number of us assumed that the Taliban was too enmeshed in Afghan society to just disappear.” [...]
The American sense of victory had been so robust that the top C.I.A. specialists and elite Special Forces units who had helped liberate Afghanistan had long since moved on to the next war, in Iraq.
Those sweeping miscalculations were part of a pattern of assessments and decisions that helped send what many in the American military call “the good war” off course.
Just about the only place in the United States where you saw substantial opposition to the Afghanistan War back in the day was on college campuses. That, conveniently enough, is exactly where I was at the time, so I got to participate in a lot of arguments on this subject. One thing I'm fairly sure absolutely nobody ever pitched to me was "well, don't you see that if we invade Afghanistan we're just going to wind up failing to achieve any of our key strategic objectives because the administration will divert crucial resources and attention to invade Iraq instead?"
That, after all, would just be ridiculous. And yet it appears to be exactly what's happened.