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Growing numbers of Americans are starting to doubt whether we should have troops in Afghanistan and whether the war there is even winnable.

We are confident that not only is it winnable, but that we have no choice. We must prevail in Afghanistan.

We went to war there because the 9/11 attacks were a direct consequence of the safe haven given to al Qaeda in that country under the Taliban. We remain at war because a resurgent Taliban, still allied with al Qaeda, is trying to restore its brutal regime and re-establish that country as a terrorist safe haven.

It remains a clear, vital national interest of the United States to prevent this from happening. Yet...