President Barack Obama is assessing whether to deploy additional combat troops and resources to Afghanistan. As long as the mission is clear and a viable exit strategy is developed with benchmarks to measure success and failure, we should fully implement a counterinsurgency strategy that should have been executed years ago.

I understand that the public and policy makers alike are weary of war and wary of quagmire, but we cannot allow past mistakes -- in Afghanistan, Iraq and elsewhere -- to deter us from the worthy, winnable and necessary task before us.

We face a stubborn enemy, but not the legendary forces of Afghanistan that expelled the Soviets and humbled the British Empire. Nor do we face another Vietnam.

The Taliban number only around 20,000 -- less than a tenth of the size of the Afghan insurgency against the Russians -- and unlike the mujahideen or Viet Cong, they are not backed by a world superpower.

The Taliban have no urban support, are ethnically exclusive and are massively unpopular across Afghanistan. As much as 70 percent of the Taliban's modest forces are not ideologically committed, but simply taking advantage of one of the few ways to draw a paycheck in one of the world's poorest countries. The average Taliban foot soldier earns three times a police officer's salary.

The other element missing from historical parallels is Pakistan, which has become the real focus of our efforts in the region and where al-Qaida currently has a "safe haven."

Pakistani intelligence actually helped create the Taliban and other extremist groups during the Soviet conflict. Now, those groups plot against not only India and the West, but Islamabad as well. Pakistan is in real danger of becoming a failed nuclear state -- Taliban and allied extremists assassinated Benazir Bhutto, rule large swaths of territory, launched attacks on Pakistan's nuclear facilities and recently advanced within 60 miles of the capital.

Pakistan has repeatedly brokered deals with the Taliban and its security and intelligence forces have often overlooked or even abetted terrorists. Only now is Islamabad beginning to recognize that its greatest threat comes not from India, but from domestic terrorists it helped create.

Pakistan is showing a new willingness to move decisively against the Taliban and the extremists that straddle the Afghanistan-Pakistan border, but it is unlikely to succeed without reciprocal American support. Our forces cannot operate in Pakistan, theirs cannot operate in Afghanistan and neither can prevail if the adversary can move back and forth across the border.

As we broaden our commitment in the region, we must also narrow the mission. Establishing good governance and functional democracy in Afghanistan will, as the country's recent election demonstrated, be an ongoing process. But that is a problem for the Afghan people to resolve and cannot be imposed by our forces.

Our mission is realistic: We are not up against an intractable enemy and we are not seeking idealistic transformation of a complex and troubled region. We must utilize Afghanistan as a base from which to achieve our objectives of helping deny al-Qaida safe haven in Pakistan and creating a probability that conditions we leave behind will not invite them to return to Afghanistan. That means neutralizing the 30 percent that is the radicalized core of the Taliban while providing the necessary security for other elements of our power -- the training of Afghan forces and socioeconomic efforts -- to advance these goals.

These are realistic, attainable and crucial goals, but we need a measured increase of boots on the ground and the right counterinsurgency strategy to achieve them.

This cannot be an open-ended engagement. Our exit strategy must have benchmarks of success or failure so that if we are not making progress toward our goals we can shift to an alternative, but potentially less-effective, containment strategy.

Opponents of increasing combat troops have proposed accelerating training of Afghan forces instead. Bolstering army and police units will be a centerpiece of the new strategy, but we cannot just place added resources into the Afghan military and expect them to swiftly carry out effective missions on their own. As the U.S. commander in Afghanistan, Gen. Stanley McChrystal, stated in his recent report: "The status quo will lead to failure if we wait for the [Afghan forces] to grow."

Similarly, we cannot rely only on air power and missile strikes. Our lack of sufficient ground forces has already resulted in three times the number of these strikes as in Iraq. These operations cause the majority of coalition-inflicted civilian causalities and are a considerable threat to popular support. An investigation is currently under way into a NATO air strike that may have killed as many as 150 civilians and has become a rallying point for the insurgency.

Finally, some have wondered whether our presence in Afghanistan is indispensable in the fight against al-Qaida. The answer is yes. We are fighting the enemy that struck us on 9/11. We cannot leave them in the same havens and hideouts they were in eight years ago and then tell the American people we have made them safe.

We allowed politics to lead us tragically into Iraq. We certainly cannot allow politics to lead us tragically out of Afghanistan when we have a measured strategy that can work. If we allow our nation to be struck again, what will we say to history?

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