Scholars have spent decades trying to answer a deceptively simple question: what explains Americans’ willingness to support the use of military force? Each year, in my War and Public Opinion seminar, students test those theories against historical and comparative cases and against the realities of international politics in almost real time. What theory offers is a way to look beyond the personality of any one leader and focus instead on the conditions under which presidents can build, sustain or lose public support for war.
Three conditions have historically helped presidents build support for the use of military force: generating public backing before a conflict begins, framing the war’s aims in terms Americans are predisposed to accept and settling on a stable and consistent explanation of what the war is for. The 2026 war with Iran—which has moved into an uncertain diplomatic phase—is an especially revealing case, because the Trump administration departed from the historical pattern.
The missing prewar moment and absent rally
Wars lose support over time. Public support for the use of military force must be built before the bombing starts. This process typically includes visibly and credibly pursuing crisis diplomacy, consulting with allies and Congress and direct presidential communications. None of that guarantees support. But it meets people’s skepticism with explanation, often enough to give an administration the benefit of the doubt in a conflict’s early stages.
Consider the 1991 Persian Gulf War. In the months leading up to the invasion, George H.W. Bush built a multinational coalition, exhausted diplomatic options and prepared the public for the possibility of a difficult fight. Even the 2003 Iraq War, despite a rationale that proved deeply flawed, involved a six-month campaign to justify the war, following a similar pattern. Americans eventually turned against it, but public support held for nearly a year before eroding. The Trump administration skipped this groundwork entirely.
The absence of a significant rally-round-the-flag effect at the initiation of the Iran war was not surprising. Rallies depend on an information environment in which the president’s framing dominates and elite cues cross partisan lines. In a country as polarized as the United States, those conditions are hard to create. Even so, some movement among independents and persuadable Republicans was possible. The absence of even that modest shift shows how little persuasive ground the administration gained at the outset.
How a war is framed at initiation and the proliferation of objectives
Americans have historically been more willing to support military force when it is understood as self-defense or as a response to a clear and present threat. Support is harder to build when the objective appears coercive or open-ended, such as toppling a government, forcing capitulation or remaking another country’s political order.
This was true before the “forever wars” in Iraq and Afghanistan, but it’s arguably more true now. Those wars, which spanned multiple administrations, involved a variety of shifting objectives. However, the case laid out by the George W. Bush Administration at the initiation of both was clear and disciplined. The invasion of Afghanistan responded to a clear threat, and the objectives were initially limited. The invasion of Iraq required a concerted effort to persuade Americans that a preemptive attack was warranted. That effort consistently framed military action as defensive in nature.
At the outset of the Iran war, the Trump administration presented five objectives: destroying Iran’s missile program; annihilating Iran’s navy; neutralizing Iran-backed proxies; preventing Iran from obtaining a nuclear weapon; and, finally, encouraging the Iranian people to overthrow their government.
Some of these aims were far more likely than others to command public acceptance. Preventing attacks on American forces, countering proxy threats and stopping Iran from acquiring a nuclear weapon could all be understood, at least in principle, through the familiar language of defense and threat prevention. By contrast, calls for overthrowing the regime pointed toward a much more expansive and politically hazardous conception of the war, one closer to regime change than limited deterrence. Destroying Iran’s missiles might plausibly fit within a narrow military rationale; annihilating its navy suggested a wider campaign with less obvious limits.
That mix mattered. The problem was not simply that the administration’s stated objective changed over the six weeks of bombing, though it did. It was that from the opening hours of the conflict, the war was framed through multiple, only partially compatible goals, each implying a different theory of victory and a different endpoint. Even Americans inclined to support the president could reasonably struggle to know what, exactly, they were being asked to support.
The limits on a president’s capacity to persuade
Presidential persuasion is most effective in the prewar moment, when the meaning and purpose of a conflict are still politically malleable. Once hostilities are underway, that room for persuasion narrows. Events on the ground can still matter, but they are less likely to fundamentally reorder public judgment than to confirm or intensify views that were already taking shape in the prewar moment.
Before the war began, more Americans already opposed it than supported it. In the six weeks of the bombing campaign, that opposition solidified into a clear majority. While some Americans remained open to limited force, support for sending U.S. ground troops was vanishingly low, and overwhelming majorities said they wanted the war brought to an end quickly. These numbers did not shift with battlefield developments.
Public opinion does not dictate foreign policy…But it does shape the boundaries of what is politically sustainable.
Public opinion does not dictate foreign policy, and presidents retain wide latitude in the use of force. But it does shape the boundaries of what is politically sustainable. Whatever happens in the coming weeks diplomatically or militarily, the public mood has been remarkably consistent: Americans have shown little appetite for a broader war, especially one involving ground troops or an open-ended campaign. If anything, the central question is not whether battlefield or diplomatic developments will generate new support for escalation, but whether they will further expose the gap between external pressures and a stable domestic preference for restraint.
Professor Erin E. Hurley is an adjunct faculty member at the School of Foreign Service at Georgetown University, where she teaches an annual undergraduate seminar on war and public opinion. She is writing a book on Americans’ post-9/11 attitudes toward the use of military force.