With respect to Iraq, the circumstances did eventually change. An exogenous event–the massive terrorist attack against America 12 years ago today–made U.S. leaders and voters far more inclined toward decisive action. The U.N. resolutions helped set the stage, as Saddam’s history of defying them provided the casus belli. The Russians and French didn’t agree on that last point, but their objections were futile. American determination to remove Saddam was sufficient to get it done.

Could that history repeat itself? At this juncture it seems highly implausible. But then how plausible would the events of 2002-03 have seemed from the perspective of, say, 1998, when Congress enacted the Iraq liberation Act, which ostensibly made regime change official U.S. policy?

Our point here is not to argue that such an eventual outcome in Syria is likely or even desirable, merely to point out that history has a way of surprising us, so that one should be cautious about projecting current trends and attitudes into the future. If you have a time machine, try this experiment: Set it for February 1989, just after the Soviet withdrawal from Afghanistan. Tell a dozen random people then that in 12½ years the U.S. and its allies will stage their own full-scale invasion of Afghanistan. Return to the present and let us know how they reacted to that prediction.

If you don’t have a time machine–and you don’t–the thought experiment will have to suffice.