WASHINGTON – Osama bin Laden was why the United States went to war in Afghanistan. His death, coming at a moment when President Obama is considering the size and speed of his promised troop drawdown in the increasingly unpopular conflict, seems likely to change the calculation surrounding any exit strategy.

The question is: Will it accelerate or put the brakes on that withdrawal?

Obama had set this summer for beginning to pull U.S. forces out of Afghanistan. But with influential Pentagon voices resisting any dramatic move, expectations had been growing that the pullout would be more gradual than many of his fellow Democrats had hoped.

At the heart of the debate is the question of what the real goal is in Afghanistan: rooting out al-Qaida, or the trickier, more ambitious aim of counterinsurgency, which requires a prolonged engagement aimed at bolstering and legitimizing the country’s government.

Less than a day after Obama announced that bin Laden was dead, both sides of that debate contended that the al-Qaida leader’s removal bolstered their own approach.

Those who had been the champions of the president’s fall 2009 decision to send 30,000 additional troops to Afghanistan insisted that the removal of bin Laden should be seen as evidence the current strategy is working and an argument for continuing it.

“I think the killing of bin Laden gives us increased momentum for the war in Afghanistan,” said Sen. Joe Lieberman, I-Conn., chairman of the Homeland Security Committee. “If I were (Taliban leader) Mullah Omar, I’d be frightened right now.”

But Senate Armed Services Committee Chairman Carl Levin, D-Mich., who opposed the troop surge, insisted he still believes Obama will begin a “robust reduction” in July.

At a minimum, the development seems likely to have given the president more credibility on the issue — and more political maneuvering room.

Polls have shown a combat-weary public souring not only on what the president had called “the war we have to win,” but also on the commander in chief’s leadership of it as it approaches the beginning of its second decade.