President Obama's long-awaited announcement of atroop drawdown in Afghanistan was in part driven by budgetary concerns.

Public opinion is turning against the war, and its immense costs are part of the reason. For example, a recent Pew poll found that 60% of Americans think that the two wars have contributed "a great deal" to the national debt, a significantly higher percentage than those choosing what they saw as the next most likely cause, the state of the national economy. And members of Congress are increasingly critical of a war with a tab that is now running at about $10 billion per month.

One specific sign of opposition was a recent resolution by the U.S. Conference of Mayors calling for "efforts to speed up the ending of these wars and . . . to bring these war dollars home to meet vital human needs, promote job creation, rebuild our infrastructure, aid municipal and state governments, and develop a new economy based upon renewable, sustainable energy."

This all leads to a basic question: how much money will the president's drawdown plan -- which calls for pulling out 10,000 troops this year, and another 23,000 by next summer -- actually save?

When the 30,000 troop surge began last summer, the administration indicated that it would cost about $1 million per troop per year, and the budget was increased accordingly, by $30 billion. But it doesn't work that way in reverse. There is some basic infrastructure that will stay in place to sustain the remaining troops, and it's not possible to shave off a percentage of that cost that is equivalent to the number of troops coming home. And as Christopher Hellman has pointed out in ablog post on the web site of the National Priorities Project, there are also likely to be costs entailed in stepped up training of Afghan troops and using private contractors to do some of the tasks that were carried out by the troops being withdrawn.

Even given all of these residual costs, the withdrawal of 30,000 troops could still save on the order of $15 billion or more per year based on similar experiences in Iraq, adjusted downward to account for the higher costs of keeping tens of thousands of troops behind in Afghanistan. This is no small sum at a time when basic governmental functions like protecting our air, water, and food supply from pollutants, providing teachers for our kids, and paying police and firefighters to supply security for our communities are all under threat from deficit-driven budget cuts.

But looked at in another way, the $15 billion in potential savings from the president's drawdown is a modest sum indeed: it's slightly over two per cent of the roughly $700 billion per year the United States is now spending for military purposes. And it's not even a down payment on the wide-ranging public investment agenda supported by the U.S. Conference of Mayors.

There won't be large scale savings from the winding down of the Afghan war until virtually all U.S. forces are withdrawn. Even then there are still likely to be ongoing costs for training, equipping and possibly even paying Afghan security forces, which could cost up to $10 billion or more per year if current rates are maintained. But the vast bulk of the $120 billion per year now being spent on the war will be freed up for other purposes: deficit reduction, or public investments, or some combination of the two.

An end to the Afghan and Iraq wars may also open the way to a more comprehensive public debate on the Pentagon's $550 billion-plus annual base budget -- a sum over four times as large as what we spend on the wars. Politically, making real cuts in Pentagon spending during a time of war is a tough sell, even given our current budgetary predicament. But an end to the wars combined with the pressure from the deficit could lead to real cuts in the Pentagon's base budget as well, especially if we adopt a new strategy that forswears major wars of occupation or large-scale insurgency campaigns of the kind our nation has waged in Iraq and Afghanistan. If we cut the war spending and bring the Pentagon's larger budget into line with reality, then we'll be talking real money.