When there is no good solution to a problem, a president has three options. One is to avoid the problem. The second is to pick the least bad of the available options. The third is to mix and match among the proposed solutions and minimize the long-term damage any decision will cause.

Afghanistan has presented President Obama with exactly this situation, and he is soon likely to settle on something closest to the third approach. This will make no one very happy. Yet it might be the least dangerous choice.

If we wanted to be successful in Afghanistan, we wouldn't choose to start from where we are now. We wouldn't have put this war on the back burner for so long, and we would have dealt much earlier with the debilitating deficiencies of President Hamid Karzai's government.

Obama can change none of this. And unlike enthusiasts for an all-out counterinsurgency strategy, Obama knows he has to make a decision that's sustainable over the long run, which means taking into account domestic economic and political realities.

One of these is the weariness over a truth that Andrew Bacevich, the hardheaded foreign policy analyst, put more plainly than most: "that permanent war has become the de facto policy of the United States."

Americans have always been willing to battle terrorists. What they did not count on—and were not led to expect when the Bush administration committed troops first to Afghanistan and then to Iraq—were two long, violent, indefinite occupations costing thousands of lives and hundreds of billions of dollars.

Advocates of a big counterinsurgency strategy are offended at anyone who raises the financial costs of our commitments. Those most angered by any talk about the immense expense of these wars are typically the very conservatives who bemoan America's fiscal condition and the dangers of long-term deficits—yet had no qualms over starting two wars and cutting taxes at the same time.

The costs are definitely worrying Obama and getting under the skin of congressional Democrats tired of attacks on their fiscal credentials. That's why it's significant that a group of House Democrats led by Rep. David Obey, D-Wis., chose last week, in anticipation of the president's decision, to introduce a bill requiring the president to set a surtax to pay for war costs in Afghanistan.

"As we've struggled to pass health care reform, we've been told that we have to pay for the bill," the Democrats said in a statement. "Regardless of whether one favors the war or not, if it is to be fought, it ought to be paid for."

The proposal may never become law but it sends a clear message: Any troop increase Obama proposes will be wildly unpopular with a large share of those who have been his strongest backers—and most popular with those whom he cannot count on for support in any other area.

Obama knows that patience with permanent war is wearing out. This is why he will insist that he is not committing new troops indefinitely. 

One senior administration official, emphasizing that final choices have not been made, described the policy Obama is likely to announce in early December this way: "It will not be open-ended, it will be limited in time, and the focus will be on strategy, not the number of troops." It's likely that the number of troops he'll send will be below the 40,000 proposed by Gen. Stanley McChrystal. 

The president has decided that Afghanistan is neither Iraq nor Vietnam. This is a view that puts him at odds with both the hawks, who constantly use the 2007 Iraq surge metaphor, and the doves, who constantly look to Vietnam as a cautionary tale.  

Obama insists that a surge in Afghanistan cannot work in the same way it did in Iraq because conditions on the ground are so different. Yet in the wake of 9/11, he sees the United States as having vital interests in Afghanistan that it did not have in Vietnam: the need to defeat terrorists in both Afghanistan and Pakistan, and to be mindful about the impact of our choices on the future of Pakistan.

No issue has presented a tougher test for Obama's non-ideological pragmatism than Afghanistan. Those with the greatest political stake in the debate reject the middle ground and doubt the president can think his way around the all-in-or-all-out dilemma. Yet this is exactly the kind of thinking Obama promised last year, and he's right to try to make it work.  

(c) 2009, Washington Post Writers Group

Related: Andrew J. Bacevich, The War We Can't Win
Joel Hafvenstein, The Cost of Peace
The Editors, Why Are We There?

Read more of our Afghanistan coverage here.