Politics matters in war. It's why the Army Chief of Staff after Vietnam tried to institute a doctrine where the nation only makes large or prolonged military commitments using all forces, including those in the National Guard and Reserves.

But the politically expedient path to draw down U.S. forces in Afghanistan more quickly than military commanders suggest -- and at increased risk to a very small share of our population -- could lead to unintended consequences. It could also lead to prolonged operations that would've otherwise been unnecessary, or jeopardize success made over the past year.

The rapid draw-down broadcasts a stronger American commitment to withdrawal than long-term stability of Afghanistan. Our urgent pullout is likely to bolster Al Qaeda and Taliban morale, weaken our allies' resolve, discourage Pakistan from cracking down on Taliban leaders in its country, and spook local Afghans who've been our partners.

The U.S. mission in Afghanistan is directly linked to our vital national interests of keeping the homeland safe from attack. It is not a luxury.

The assumption that Afghan draw-down savings could then be applied, dollar for dollar, to domestic spending is a false choice. Until a few years ago, combat operations in Afghanistan were debt financed.

Once the mission going forward -- still unclear -- transitions more over time to counterterrorism operations, they still won't be cost free. Additionally, the cost of redeploying forces is much more than the cost of keeping them in theater.

America's ground forces are exhausted, their equipment old and depleted. The Army and Marine Corps in particular now need to reinvest in their people, in tracked and wheeled vehicles, and in helicopters -- after being employed at wartime-usage rates for a decade and in harsh conditions.

Any cost "savings" from our Afghan drawdown will not materialize for several years after combat has ended -- if we're honest about the accounting and make the reset of the Army and Marine Corps a real priority.

Mackenzie Eaglen is a research fellow in foreign policy studies at The Heritage Foundation.