Forty years ago this week, Americans realized that their country was not going to win the Vietnam war. Lulled by assurances that “progress” was being made in the fight against the insurgents, Americans had patiently borne five years of growing military casualties in Vietnam, but the Tet Offensive shattered their illusions. Could the same thing happen this year in Iraq?

Paradoxically, the Tet Offensive was a military disaster for the Viet Cong. They threw 45,000 of their most experienced soldiers into simultaneous attacks in more than 100 cities and towns on January 31, 1968, believing that they could trigger a nationwide popular uprising against the Americans.

There was no national uprising in South Vietnam; the communists had overestimated their support in the cities. After Tet, the Viet Cong was so weakened that the North Vietnamese regular army had to take over more and more of the fighting — but Tet was a decisive political defeat for the US.

1968, like 2008, was an election year in the US, and Tet made it plain to voters that while the Vietnamese insurgents might not be able to drive the Americans out, they could go on fighting them indefinitely. By the end of March, 1968, President Lyndon Johnson had abandoned his re-election campaign and offered to open negotiations with the North Vietnamese. Richard Nixon won the presidency that November on a promise to withdraw American troops from Vietnam (although it took him five years to keep it).

Many people in the West believed at the time that the wily Vietnamese communists had foreseen all this, but they didn’t. General Tran Do, one of the planners of Tet, later said: “In all honesty, we didn’t achieve our main objective, which was to spur uprisings throughout the South.... As for making an impact in the United States, it had not been our intention — but it turned out to be a fortunate result.”

Defeat is triumph

The lesson of Tet is that Western troops fighting in Third World countries can win every battle, but they are terribly vulnerable on the political front. The insurgents don’t have to win. They only have to show that they can go on fighting indefinitely, because the Western country involved always has the option of cutting its losses and bringing its troops home. The insurgents are not really going to “follow us home” (as President George W. Bush occasionally argues), so sooner or later the option to withdraw will be exercised.

Something like the Tet Offensive can be a catalyst for that kind of shift in opinion on the occupying power’s home front. So, who in Iraq might be tempted to try a ‘Tet Offensive’ in this US election year?

Not the Sunni Arabs who did most of the fighting against the US occupation in 2003-2007, for they have now been drawn into anti-al Qaida, anti-Shia militias backed by the US. They may turn on their paymasters eventually, but not yet.

Not the traditional Shia religious parties that now dominate the Iraqi government either. They already have most of what they want, and they still need American protection. Certainly not the Kurds, the one pro-American group in Iraq. But how about Moqtada al-Sadr and his Mehdi Army, the largest militia in Iraq?

Al-Sadr will go on being marginalized by the conservative Shia establishment, unless he can position himself as the patriot who defied the Americans while everybody else was playing along with them. His Mehdi Army has observed a self-imposed ceasefire since last August, but he could break it at any time.

If the Mehdi Army launched an Iraqi version of the Tet Offensive, it would be defeated as badly as the Viet Cong. But everybody who knows that history understands that military defeat can lead to political victory. The temptation is there, but al-Sadr won’t do it now. August or September, however, could be another matter entirely.