Bill Quick does a good job of explaining why Americans are growing weary of the war on terror, and I think we can learn a lot by flipping the question around.
The problem is three years of what appears to be bumbling, fumbling, softness, lack of clarity, lack of purpose, and lack of will. The public will grow tired of any enterprise when it appears that those who purport to represent it have utterly lost their way. This is the "leadership problem" in a nutshell. As I have repeatedly stated, leaders find a way to lead. Losers find excuses. Eventually the public tires of excuses. ...
If you want Americans to sacrifice "blood, toil, tears, and sweat" to destroy a "civilizational enemy," then you have to name that enemy, describe its places of power, and be honest about how far you will go - and may have to go - to achieve victory. The pabulum about diplomacy and democracy may seem politically expedient in the short run, but in the long run it has sapped the will of Americans to fight the necessary - and very real - battles that must be waged in order to win the war at all.
To look at it from the other side, why aren't the Islamists growing weary of the war? They're taking far more casualties than we are. They're living in caves, running and hiding, blowing themselves up, and living in the shadows just to be a thorn in our side. Their side of the war is far harder on them individually than our side is on most of us, and yet they're more keen to fight than ever. Why? Perhaps because they, unlike us in the West, know what they're fighting for and are determined to win. Their leaders have articulated why they're fighting and how they're going to win, and ours are too consumed with multiculturalism and UN nonsense to even publically define our enemy.