Try hard as you can, there doesn’t seem to be any escaping from comparing America’s eight-year war in Afghanistan to the one it fought in Vietnam.

Every now and then, either when there is a fresh setback or a key moment in Afghanistan’s turbulent history, like last week when it went to the polls to choose a president, the debate flares anew.

Foreign Policy magazine has a provocative piece headlined “Saigon 2009: Afghanistan is today’s Vietnam. No question mark needed.” No matter who wins last week’s election, America is certainly not winning the war in Afghanistan because it is committing the same mistakes it did in Vietnam, authors Thomas H.Johnson and M Chris Mason argue.

The parallels are just too strong, too structural to be ignored. Both Afghanistan and Vietrnam (prior to U.S. engagement there) had surprisingly defeated a European power in a guerrilla war that lasted a decade, followed by a civil war which last another decade. Insurgents in both enjoyed the advantage of a long, trackless and unclosable border and sanctuary beyond it, the authors say.

Both were land wars in Asia with logistics lines more than 9,000 miles long and extremely harsh terrain with few roads, which nullified U.S. advantages in ground mobility and artillery. Almost exactly 80 percent of the population of both countries was rural, and literacy hovered around 10 percent. In both countries, the United States sought to create an indigenous army modeled in its own image, based on U.S. army organization charts.

But above all, the United States has consistently and profoundly misunderstood the nature of the enemy in each circumstance, the authors say. “In Vietnam, the United States insisted on fighting a war against communism, while the enemy was fighting a war of national reunification. In Afghanistan, the United States still insists on fighting a secular counterinsurgency, while the enemy is fighting a jihad.”.  In short, it is hard, almost impossible, to defeat an enemy you don’t understand.

Already, like the Vietnam war, support is starting to dwindle at home with a Washington Post-ABC poll showing the number of Americans who believed the war in Afghanistan was worth fighting slipping to below 50 percent.

Is Afghanistan already starting to weigh on President Barack Obama, then ? The New York Times this weekend questioned whether he was fated to be another Lyndon B. Johnson,  and not another Abraham Lincoln or the second coming of Franklin D. Roosevelt as his supporters portrayed him to be even before he took office.

Each presidency is different, but it is “the L.B.J. model — a president who aspired to reshape America at home while fighting a losing war abroad — is one that haunts Mr. Obama’s White House as it seeks to salvage Afghanistan while enacting an expansive domestic program,” the newspaper said.  Obama himself  has expressed concern that Afghanistan may yet hijack his presidency, it reported based on accounts of a group of historians who had dinner with him at the White House this summer.

Like Johnson, Obama has framed Afghanistan as a war of necessity and not choice. Just as Johnson had no choice but to fight in Vietnam to contain communism,  America has to be engaged in Afghanistan as the bulwark against international terrorism.  “Those who attacked America on 9/11 are plotting to do so again. If left unchecked, the Taliban  insurgency will mean an even larger safe haven from which al Qaeda would plot to kill more Americans,” he told the Veterans of Foreign Wars at their convention in Phoenix last week.

But is it really a war of necessity ? Richard Haas, the president of the Council of Foreign Relations, argues it was necessary to go into Afghanistan in the wake of 9/11, but no longer to remain there. Wars of necessity must meet two tests, he says in an op-ed in the New York Times. They must involve vital national interests, and second, a lack of viable alternatives to the use of military power to defend those interests.

While it was necessary to invade Afghanistan to oust the Taliban,  now that there is a friendly government in Kabul is it necessary to maintain a military presence ? While it is true that the government is weak, and unable to enforce its writ in large parts of the country, it is equally true that terrorism cannot be eliminated even if you had a strong government, Haas argues.

 Militants could still operate from Afghanistan and would put down roots elsewhere. And Pakistan’s future would remain uncertain at best.

Moreover, he says  there are alternatives available.  The United States can begin to curtail  ground combat operations and emphasise drone attacks on militants, the training of Afghan police officers and soldiers, development and diplomacy to fracture the Taliban.

A more radical approach would be withdraw completely and focus on regional and global counter-terrorism efforts and homeland security initiatives to protect the United States from threats that may emanate from Afghanistan, Haas suggests, In that sense, Afghanistan would resemble the approach toward Somalia and other countries where governments are unable or unwilling to take on militants, and the United States eschews military confrontation.

But is the world ready for that ?

[Photographs of Afghan women voting, U.S. troops in Bagram and Obama in Phoenix last week]