“Pleikus are like streetcars.” That’s how McGeorge Bundy, President Johnson’s national security advisor, explained what the escalation of U.S. bombing of North Vietnam in February 1965 to had to do with the administration’s justification for it, which was a Vietcong attack on U.S. bases near Pleiku. Johnson had already decided to increase bombing, but he wanted a pretext that would make it seem defensive. Bundy meant that, absent the Pleiku attack, another incident would have come along shortly to justify additional bombing. A similar bait-and-switch is occurring today in U.S. Iraq policy.

On August 7, President Obama explained that we were bombing Iraq again to defend U.S. personnel in Erbil and rescue ten of thousands of Yazidi civilians stranded on Mount Sinjar (really mountains) and surrounded by murderous militiamen of Islamic State of Iraq and the Levant (ISIL). Now, it turns out there were far fewer Yazidis on the mountain than the administration claimed; they are mostly out of harm’s way, and the threat to Erbil has ebbed.

With the two goals he set for bombing achieved, the President quickly offered a third. In the letter sent to Congress on Sunday (pursuant to the War Powers Resolution, which he flouts when it’s inconvenient) the President argued that U.S. bombing would help “Iraqi forces” retake the Mosul dam. Kurdish Peshmerga and Iraqi Special Forces have now done that.

Monday, the President again broadened the bombing’s objectives. The airstrikes against ISIS still protect U.S. personnel and serve humanitarian purposes, he said, but now, it seems, those are general goals that ongoing bombing serves. The President also suggested that ISIS is a security threat to the United States. Not for the first time, he said that once the new Iraqi government forms, we will “build up” Iraqi military power against ISIS.

Only the speed of this slide down a slippery slope is surprising. As I recently noted, the humanitarian case for protecting the Yazidi easily becomes a case for continual bombing of ISIL and resumed counterinsurgency war in Iraq. Their danger to civilians was never limited to Sinjar. And as in Syria, the major humanitarian threat in Iraq is civil war.

Americans, the president included, need to admit being out of Iraq potentially means letting it burn. The collapse of the fiction that U.S. forces stabilized Iraq before exiting forces us to confront the unpleasant contradictions in U.S. goals there. We want to avoid the tragic costs of U.S. forces trying to suppress Iraq’s violence. We want a stable Iraqi federal government and we want Iraqis to live peacefully. Each of those goals conflicts with the others.

Even if the new Prime Minister is amenable to Sunni demands, U.S. bombing is unlikely to allow Iraqis to destroy ISIL and its allies. Large-scale violence will likely continue. Suppressing insurgency will likely require resumption of U.S. ground operations. And even that, we know, may not help much. Centrifugal forces in Iraq will remain strong, especially now that we are arming the Kurds. Vesting federal power in Prime Ministers that are inevitably Shi’ite makes continual sectarian fights likely.

We should know by now that we lack the ability to stabilize Iraq at acceptable cost. We should also know that the primary threat to U.S. security in Iraq is the temptation to try to forcefully run it. Knowing these things means accepting some tragedy in Iraq.