The president, who addressed the nation in a prime-time speech from the White House, stopped short of declaring victory, but he suggested that the mission had been a success and that it was time to turn to a new foreign policy and to place a greater focus on domestic concerns.
A debate inside the Republican Party over Afghanistan, along with larger questions about American military engagement, has changed the political dynamic facing Mr. Obama as he prepares for re-election. He made clear that he would not be haunted, like many Democrats before him, by being cast as weak on national security. But he pledged to ?chart a more centered course,? a phrase that could well serve as a metaphor for how he has sought to reset his presidency after Democrats were soundly defeated last fall.
Mr. Obama is benefiting from a confluence of factors ? a rising strain of Republican isolationism, the killing of Osama bin Laden and deep concerns about spending and the deficit ? which provide unexpected flexibility for dealing with Congress and selling his decision to the nation. He will test whether the post-Sept. 11 politics have changed enough to allow a Democratic president to wind down a war with little or no political peril.
?These long wars will come to a responsible end,? Mr. Obama said. ?As they do, we must learn their lessons. Already this decade of war has caused many to question the nature of America?s engagement around the world.?
As the nation has grown weary over the cost and toll of war, fault lines have emerged among Republicans, with the longstanding isolationist strain regaining its footing after the Sept. 11 terrorist attacks and the adventurism of the George W. Bush era.
The aggressive posture adopted by the president, particularly in pulling out troops faster than Pentagon advisers recommended, could open a discussion in Congress and on the presidential campaign trail. Republicans now hold an array of positions, from the budget-minded focus of the Tea Party movement to the stay-the-course view of the party?s 2008 nominee, Senator John McCain of Arizona, to other internationalist Republicans who fear the party has lost its way.
For the first time in generations, neither the president nor any candidates for the office have worn the military uniform. The familiar chords of patriotism may have given way to increased concerns about priorities at home.
Mr. McCain has emerged as the leading critic of Mr. Obama?s decision on Afghanistan, but his views are muted by the many Republican presidential candidates who have expressed a desire to end the war as soon as possible.
Jon M. Huntsman Jr., a former Utah governor who recently stepped down as the ambassador to China, is trying to build his Republican presidential campaign around his foreign policy experience, which included positions in both Bush administrations. Four years ago, he was Mr. McCain?s co-chairman, but now is seeking to distinguish himself on Afghanistan by raising questions about whether the country can afford it.
?It is time we move to a focused counterterror effort, which requires significantly fewer boots on the ground than the president discussed tonight,? Mr. Huntsman said.
Tim Pawlenty, a former governor of Minnesota, has emerged as one of the party?s few candidates who are cautioning against an abrupt withdrawal in Afghanistan. ?I?m concerned about what appears to be a drift toward minimalism and isolationism inside the Republican Party,? Mr. Pawlenty said Wednesday in an interview. ?But it?s really important to make sure that we finish the job correctly in Afghanistan.?
Geoff Garin, a Democratic pollster who has conducted focus groups to gauge public opinion of the war, said the multiple messages among Republicans would benefit Mr. Obama.
For Mr. Obama, his prime-time announcement was the latest in a series of defining moments in his presidency. Four years ago, in the early stage of his political rise, he positioned himself as a strong opponent of the Iraq war. After he took office, he began delivering on his pledge to end the war. But he chose to build up efforts in Afghanistan, infuriating many Democrats by sending 30,000 more troops.