Calls are mounting in Congress (and among some influential opinion groups) for escalating Washington’s military intervention against ISIS in Iraq and Syria and for possible military action against Iran if the new nuclear agreement with that country falls apart. Caution lights should be flashing about both the extent and durability of such sentiment for military action. As I note in a recent article in the National Interest Online, this country has an unfortunate history of launching ill-considered armed crusades, often initially with enthusiastic public support. But that support has a tendency to evaporate and turn to bitter recriminations unless certain conditions are met. Policymakers need to appreciate that history as they consider intensifying U.S. involvement in the Middle East’s turbulent affairs.

Because most Americans believe that the United States embodies the values of individual liberty, human rights, and government integrity, a foreign policy that seems to ignore or violate those values is almost certain to lose the public’s allegiance sooner or later. That is what happened with such missions as the Vietnam War, the Iraq War and, more recently, the counterinsurgency war in Afghanistan. It is not merely that the ventures failed to achieve quick, decisive results, although that aspect clearly played a role. It was also that the United States was increasingly seen as expending blood and treasure on behalf of odious clients and dubious causes that had little or nothing to do with the republic’s vital interests. A disillusioned public turned against those missions, and that development created or intensified bitter domestic divisions.

To sustain adequate public support for military ventures, the objective must be widely perceived as both worthy and attainable. Without those features, public support for a policy either proves insufficient from the outset or soon erodes, and either development is fatal in a democratic political system.

Preserving public support requires officials to make an honest assessment of the issues at stake. Too often, both during the Cold War and the post–Cold War eras, U.S. policymakers have hyped threats to American interests. The alleged dangers posed by such adversaries as North Vietnam, Serbia, Saddam Hussein, the Taliban, and Syrian dictator Bashar al-Assad bordered on being ludicrous. At times, it appears that U.S. officials have deliberately engaged in distortions to gin-up public support for purely elective wars. On other occasions, officials seem to have succumbed to their own propaganda. In either case, public support dissipates rapidly when evidence mounts that the supposed security threat to America is exaggerated.

That troubling history should reinforce the need for caution as U.S. leaders consider new military interventions, especially in the Middle East. None of the proposed missions is likely to produce quick, decisive results—much less results with modest financial outlays and minimal casualties. Moreover, escalating America’s involvement in the region’s myriad troubles puts the United States in a close de facto partnership with Saudi Arabia and its Gulf allies—some of the most corrupt, brutal governments on the planet. Publics in the Middle East and around the world are watching, and the potential for unpleasant blowback is extremely high. And as we saw with the wars in Vietnam, Iraq, and Afghanistan, the reaction of the American people to associations with sleazy foreign clients can become one of profound revulsion. The conditions are in place for new foreign-policy debacles, if U.S. officials have not learned the appropriate historical lessons.