Soldiers with Bravo Company 82nd Division Special Troops Battalion provide security during an air assault mission in Parwan, Afghanistan.
The 2001 invasion targeted al-Qaida and its Taliban allies shortly after the Sept. 11 attacks on the United States, which claimed nearly 3,000 lives.
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Victory in Afghanistan seemed to come quickly. Kabul fell within weeks, and the hardline Taliban regime was toppled with few U.S. casualties.
But the Bush administration's shift toward war with Iraq left the Western powers without enough resources on the ground, so by 2006 the Taliban had regrouped into a serious military threat.
Obama deployed more troops to Afghanistan, and casualties increased sharply in the last several years. But the American public grew weary of having its military in a perpetual state of conflict, especially after the withdrawal of American troops from Iraq at the end of last year. That war, which began with a U.S.-led invasion in 2003 to oust Saddam Hussein, cost the lives of nearly 4,500 U.S. troops, more than twice as many as have died in Afghanistan so far.
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Although Obama has pledged that most U.S. combat troops will leave by the end of 2014, American, NATO and allied troops are still dying in Afghanistan at a rate of one a day.
Even with 33,000 American troops back home, the U.S.-led coalition will still have 108,000 troops — including 68,000 from the U.S. — fighting in Afghanistan at the end of this year. Many of those will be training the Afghan National Security Forces that are to replace them.
"There is a challenge for the administration," O'Hanlon said, "to remind people in the face of such bad news why this campaign requires more perseverance."
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Associated Press writers Heidi Vogt and Rahim Faiez in Kabul and researcher Monika Mathour in Washington contributed to this report.
Copyright 2012 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.
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