Eight years ago this week, Osama bin Laden watched and then celebrated as a terrorist attack he had authorized brought down the World Trade Center and part of the Pentagon, slaughtering thousands of innocent Americans.

Bin Laden was, at that time, in Afghanistan, which was, at that time, ruled by the Taliban. Soon, U.S. forces and their anti-Taliban Afghan allies would topple the Taliban. Bin Laden and Taliban leader Mullah Omar would flee across the mountainous border into the wild, tribal areas of northwest Pakistan. From that base, they would organize an insurgency against U.S. and NATO forces and a new Afghan government.

Conservatives are now divided over this conflict. The debate on the right is interesting but academic: Barack Obama - no conservative -- is president. During his campaign for the White House, he blasted President Bush for diverting to Iraq resources needed for Afghanistan, the "good war," the war that, he emphasized, must be fought and won. Since becoming president, Obama has named his own commander for Afghanistan, Gen. Stanley McChrystal, and earlier this year he sent 21,000 additional troops, a down payment on the increased resources needed to turn the tide.

But if Obama intends for this mission to succeed, it will require more than boots on the ground and drones in the air. He also will have to use his not inconsiderable powers of persuasion to make the case that Afghanistan is both worth winning and winnable. If he can not bring himself to do that - with at least as much passion as he's put into more than 100 speeches on health care - support for the fight in Afghanistan will collapse, and nothing pro-mission conservatives say, write or do can prevent it. Does history offer any precedent of an ambivalent commander-in-chief leading a nation to victory in war?

Columnist George Will has made the conservative critique forcefully, contending that American troops are not so much battling America's enemies in Afghanistan as nation-building and democracy-promoting -- Sisyphean tasks at best in such a remote corner of the world.

Pro-mission conservatives argue that promoting economic development and improved governance are simply components of counterinsurgency, the method of warfare - as we learned the hard way in Iraq - most likely to succeed against militant jihadis on Third World battlefields.

I would stress this: Afghanistan is not a war. It is one battle in what - I'm not the first to deduce - is going to be a long war, a global conflict to defend America and the West against an insidiously dangerous enemy that has emerged from within the Islamic world.

It is a war over ideas as much as it is a war over land. In fact, as real estate, Afghanistan is of minimal value. But what happens there will help determine how we - and our enemies and the millions of people around the world who have not taken sides -- understand what this struggle is about and who is likely to prevail.

"It was the Soviet withdrawal from Afghanistan that laid much of the imaginative groundwork for 9/11," Wall Street Journal columnist Bret Stephens points out. "If one superpower could be brought down, why not the other?"

Gen. McChrystal and his commander, Gen. David A. Petraeus (a brilliant military mind), know what needs to get done to win the Battle of Afghanistan. They ask only that we provide the troops, weapons and support. Continued...