With the economy still in tatters, with White House officials speaking openly about the possibility of a Republican takeover of one or both houses of Congress, with the administration frustrated by the stalling of campaign-finance legislation in the Senate, and with the president's poll numbers at alarmingly low levels, the last thing Barack Obama needs is fresh doubts about the American role in Afghanistan nourished by mischievous and misleading analogies to the war in Vietnam.
But presidents seldom get what they wish, and so right now Mr. Obama is afflicted with both -- and both are perilous not only to the Democrats' prospects in the midterm congressional elections but also to the Obama presidency.
Seldom in the course of a single week do the moorings of a presidency shift so dramatically as they did last week, when the release of thousands of documents detailing the ways of war in central Asia shook the White House -- and endangered the brittle consensus, both inside the executive mansion and out, that sent a surge of American troops to Afghanistan and that believes the improvised, crude coalition engaged in battle there can prevent catastrophe if not exactly prevail.
For a force that moved like an earthquake through capital and country, the AfPak archive produced unusual agreement: The documents didn't tell us much we didn't know. The documents didn't tell us much that comforted us. The documents changed everything.
All that and one thing more: Pakistan sure challenges the meaning of the word ally.
It doesn't matter that many of the documents released by WikiLeaks detail events that occurred during the George W. Bush administration, not the Obama administration -- just as it didn't matter that all the events detailed in the Pentagon Papers occurred during the Truman, Eisenhower, Kennedy and Johnson administrations. That mess redounded to the Richard Nixon administration, which took office two years after the end of the period covered by the Pentagon Papers.
The difficulty for the Obama war ministry is that the WikiLeaks papers outline troubling ties between the Taliban and Teheran that will unsettle Americans already worried about Iran and nuclear weapons, problems with drones that will heighten concern about military tactics in the region, attacks on civilians that war critics will almost certainly describe as atrocities, and examples of double-dealing by Pakistan that will concern everybody. Very few people, if any, have read all 75,000 documents posted online, but we await the appearance of, say, 1 percent of those documents that will comfort rather than distress American military strategists.
While these papers didn't tell us anything new, they did something potentially more damaging. They sowed new doubts among the American people about the American course.
Last week's episode included two of the important elements of the Vietnam era: leaked historical documents and a frustrating war in a faraway place in Asia. But just as Vietnam provided a convenient but inaccurate comparison for the war in Iraq, Vietnam provides a convenient but inaccurate comparison for the war in Afghanistan.
We have learned in the past three-quarters of a century to be wary of appeasement (the lesson of Munich) and to be wary of quagmires (the lesson of Vietnam) but not the more important lesson, which is to be wary of lessons.
Appeasement so marked, and so warped, American policy makers in the post-World War II period that it was a major factor behind the growing commitment to Vietnam.
"The appeasement policy of Neville Chamberlain, the British prime minister who had, with the assent of the French, delivered Czechoslovakia to Hitler at Munich in 1938, was always in the back of their minds," Neil Sheehan wrote of American leaders in "A Fiery Peace in a Cold War," his 2009 account of the development of the intercontinental ballistic missile. "Now that it was their turn to lead, they were not going to lose the peace gained by their victory over Nazi Germany and Imperial Japan through similarly weak behavior toward Stalin and the forces of 'International Communism.' "
Now the danger is that American policy makers, and the American public, might view Afghanistan through the Vietnam prism. That impulse has been reinforced by the apparent similarities between the Pentagon Papers and the AfPak papers.
But they are not similar. "They're different in every way," Leslie H. Gelb, who directed the Pentagon Papers project for the Defense Department, said in a telephone conversation last week. "These documents are from the bottom of the governmental food chain -- people in the field. The Pentagon Papers were almost all from people at the top of the governmental food chain. The WikiLeak papers are what people saw on the ground. The Pentagon Papers are what people in the stratosphere thought. One was about what people saw in battle. The other was basically elements of policy."
Dr. Gelb, later a New York Times reporter, editor and columnist, believes that the public misinterpreted the meaning of the Pentagon Papers; he said the debate spawned by the release of those documents in 1971 was more about governmental lying than about Vietnam.
"But as one of the few people who has ever read these documents, I know it shows governmental lying here and there -- but it also shows people believed what they were doing," he said. "In this case, plenty of people believe what they are doing -- and believe that our security is tied up in a mountainous place maybe not even in the 20th century yet. For them it's not a game, it's a belief."
All of which is why it is important to heed the warning of Margaret MacMillan, a historian who is now the warden of St Antony's College, Oxford. "We can draw our lessons carefully or badly," she wrote in the introduction to "Dangerous Games: The Uses and Abuses of History," published 13 months ago. "That does not mean we should not look to history for understanding, support and help; it does mean that we should do so with care."
In history as in policy, it's best to adopt the perspective of a 17th-century aphorism that has become the wisdom of the swimming hole: Look before you leap.
David M. Shribman is the executive editor of the Post-Gazette ( firstname.lastname@example.org , 412 263-1890).