Blowback. Even the most casual observer of U.S. foreign policy in recent years is familiar with the concept, if not the term. The word comes from the world of espionage and refers to an operation that blows up in the faces of those who planned it. Al-Qaida, an offspring of the U.S.-backed anti-Soviet jihad in Afghanistan, is a classic example. The Cold War-era fight against the Soviets was the foreign policy equivalent of the old American medical joke, the operation was a success but the patient died.

Now the U.S. is proposing to repeat the error at an unprecedented level. A Pentagon spokesman this week said plans are being prepared to train and arm 85,000 Pakistani tribesmen to dislodge al-Qaida and the Taliban from their safe haven in Pakistan's frontier provinces. To do that, they are planning to send in several dozen U.S. troops and spend an estimated $350 million. Think about that for a moment. American soldiers sent to a country in chaos. Tens of thousands of tribesmen trained for combat. The dangers abound. So, too, the ironies. The presence of U.S. troops in Muslim countries is a key reason for anti-Americanism. And then there is the fact that this army of would-be anti-jihadis is being built to fight the jihadis another U.S. administration trained and financed just two decades ago.

The model for the project is Iraq, where the U.S. has bought the cooperation of Sunni insurgents with money, weapons and training, producing a short-term alliance-of-convenience against al-Qaida in Iraq at the likely price of a long-term Sunni-Shiite civil war.

Like the Cold War project to bloody the Soviets in Afghanistan, this latest U.S. effort to help "us" and defeat "them" is yet another unneeded reminder of the degree to which short-term thinking too often drives U.S. policy. The enemy of my enemy may be my friend, but as Afghanistan reminds us, such alliances last only as long as they are convenient for both sides.