The debate before the president’s speech focused on the steep challenges of the war: the record American deaths this year; the heavy financial cost; and the uncertain prospect of victory. A good part of Congress, and even a couple of Republican presidential candidates, appeared ready to write off Afghanistan as a lost cause.

Obama adopted just the opposite tack: He declared victory as a way of justifying troop withdrawals that will be larger and faster than those sought by his military commanders. And he invited Americans to put ”a difficult decade” of wars behind them.

“Tonight we take comfort in knowing the tide of war is receding,” Obama told his national television audience. “The light of a secure peace can be seen in the distance. These long wars will come to a responsible end.”

That success in Afghanistan can be glimpsed — even taken as a given — will come as news to those few Americans who have followed the war closely. While there have been important tactical gains against the Taliban in southern Afghanistan, they are, as commanders frequently put it, “fragile and reversible.” The Taliban is still strong in eastern Afghanistan, and its sanctuaries in Pakistan remain mostly untouched.

American commanders, including Gen. David A. Petraeus, sought a smaller troop withdrawal this year, and a longer timetable for the removal of the 30,000 “surge” troops Obama approved in 2009, precisely because they believe the war is far from won.

Yet Obama has already moved on: He devoted much of his speech to talking about the lessons of the post-Sept. 11 wars and his hopes for the era that follows them. America should be neither isolationist nor too interventionist, he said; it should work more with allies.

Then came his punch line: “America, it is time to focus on nation building here at home.” Obama went on to talk about his favorite domestic initiatives: “rebuild our infrastructure and find new and clean sources of energy.” Suddenly, an address about troop withdrawals was sounding a lot like a campaign stump speech.

In the 1960s, then-Sen. George Aiken famously advised Lyndon Johnson that the best course in Vietnam was to declare victory and withdraw. Obama seems to have taken that maxim and applied it to Afghanistan. Only the war is far from over, victory is far from certain — and in November 2012, 68,000 Americans will still be fighting and dying.