The perceptions and the politics in the United States regarding the use of military force against the so-called Islamic State or ISIS are now clear and well-established. The issue has become a classic case of those without the responsibilities of office seizing on a matter of public fear and concern and lambasting those with such responsibilities for not doing more, with the lambasters enjoying the luxury of not having to develop specific and well-thought-out measures and not having to consider the costs, risks, effectiveness, and consequences of any such measures.

Thus we hear the Republican presidential candidates making a huge deal of what they describe as a grievous threat from ISIS and using bombastic language to let us believe that most of them would make quicker and more extensive use of military force against this group than is the supposedly reticent and weak-kneed incumbent in the White House. But despite the volume and intensity of such rhetoric we hear very little about exactly how they would use force differently and even less about how any different measures should be expected to work. Even systematic efforts to catalog what candidates have said on the subject yield mostly spotty and vaguely phrased results.

The public mood being exploited is clear enough. A recent Monmouth University poll showed 78% of respondents believing ISIS to be “a major threat to U.S. security” and 68% saying that the U.S. Government is “not doing enough to defeat ISIS.” When asked whether ISIS can be stopped without U.S. troops, can be stopped only with U.S. troops, or cannot be stopped, a plurality (47%) said only with U.S. troops.

President Obama has felt it necessary to join in some of the public chorus on this topic. After a televised address from the Oval Office did not receive good enough reviews, the president a week later spoke from the Pentagon about the military side of anti-ISIS efforts, citing numbers of bombing sorties as if that were a good gauge of making progress on counterterrorism. Then a couple of days later he made another publicly covered appearance, with additional talk about the ISIS problem, at the National Counterterrorism Center.

When we see a strong association between politicians' rhetoric and a pattern of public concern reflected in opinion polls, we need to be careful about what is cause and what is effect. Politicians exploit public beliefs, but segments of the public form many of their beliefs based on cues they get from political leaders whom they most support and political parties with which they most identify. An event such a high-profile terrorist incident can trigger a shift in mood, but then the political rhetoric and exploitation have a snowball effect. If political leaders of both parties had been making public statements much more consistent with the actual interests of the nation and what threatens those interests most severely, poll results on questions about ISIS would have been significantly different.

Perhaps the single formulation in the presidential candidates' rhetoric on this subject that has gotten most attention is Ted Cruz's recommendation to use “carpet bombing.” As Major General Robert Scales, a military historian and former commandant of the Army War College, comments, carpet bombing “is just another one of those phrases that people with no military experience throw around.” When Cruz is pressed on the subject, it becomes clear he does not know what he is talking about in his use of the terminology and doesn't actually have a plan for use of air power that looks different from what the current administration is doing.

Max Boot, in a piece that gives Cruz far too much credit for having a serious proposal for use of air power rather than merely using carpet bombing as a term that sounds tough, gives good reasons why simply bombing ISIS will not defeat it. Boot, who is a serious analyst in his own right but is identified in this article as a foreign policy adviser to Marco Rubio, ends up with a vaguely stated conclusion that U.S. ground troops will have to be sent against ISIS. Rubio's own statements on this subject also have been vague, with some references to a need for using more special operations forces.

It has been left to also-ran candidates to be at all specific about numbers of U.S. ground troops they would favor using. Lindsey Graham has used the figure of 10,000 troops; Mike Huckabee and Rick Santorum have talked about 10,000 or more. But as experience in other wars indicates and as analysis by Stephen Biddle and Jacob Shapiro concludes, one would need to add a zero and then some to get results on the ground that would be anything like what these politicians claim could be gotten through application of U.S. military force. Biddle and Shapiro write that “well over 100,000” troops would be needed in such a mission.

Meanwhile, back at the Oval Office—where the buck stops and where costs, risks, effectiveness, and consequences do need to be seriously considered—President Obama, notwithstanding his felt need to join in some of the rhetorical highlighting of ISIS and of the role military force plays in dealing with it, has shown that he has a better grasp of the realities involved than the candidates who are trying to ride the issue into the White House. The president laid out some of his thinking earlier this week in a discussion with some opinion writers that was supposed to be off the record but had much of its substance come out in a column by David Ignatius and through other participants. A fundamental basis of the president's policy is the correct judgment that ISIS, though posing a significant security problem in several respects, is not an existential threat to the United States or anything close to it, as much of the American rhetoric about the group would suggest. It thus is not worth the costs that a significantly expanded military campaign in the Middle East would entail. The president mentioned monthly costs to the United States, hypothetical but certainly plausible, of 100 dead, 500 injured, and $10 billion in expenditures.

One fundamental reason an expanded military campaign against ISIS therefore is not warranted is that to get any meaningful result it would entail far greater costs than what the politicians agitating for doing more are suggesting, and than what the American people would consider after the fact to have been a worthwhile expenditure. But even if the American people were knowingly willing to assume such a burden, another fundamental reason such a campaign would not be warranted is that it still would not, despite the heavy costs, solve the main problems—involving terrorism and instability—it would be intended to solve. In important respects it would be counterproductive. President Obama has only touched on some aspects of this latter reason, lest he be seen to go too far from what has become the rhetorical mainstream about threats from ISIS and the need to confront it militarily.

Advocacy of larger and more direct use of U.S. military force against the group rests on a notion of ISIS as a discrete set of people, places, and institutions that could be “taken out” with a concerted attack by the powerful U.S. military. John McCain, chairman of the Senate Armed Services Committee, who has mentioned the same figure of 10,000 troops as his friend Lindsey Graham, uses the “take out” concept. This is an incorrect image of ISIS. ISIS is not some discrete set of people; it is gaining and losing both leaders and recruits all the time. It is not some one place where we can play a game of capture the flag; it moves around and has been gaining and losing (more recently, mostly losing) territory throughout its history. One of the biggest chapters of that history was its move out of Iraq and into Syria when it was able to take advantage of the disorder of a growing civil war there. If a U.S. or U.S.-led military campaign captured and held Raqqa and all other cities that ISIS now controls, that would not mark the end of the campaign but only its move into a new phase. A large insurgency, or several insurgencies, would continue. “Taking out” ISIS with the capturing of cities and the occupation of territory and the driving of ISIS leaders out of whatever is their current domicile would no doubt give rise to the temptation to declare “mission accomplished” and to make celebratory flights to aircraft carriers, just as such an event once did after the invasion of Iraq. And the grounds for the celebration would be no stronger than they were in that earlier instance in Iraq.

U.S. or Western troops, even assuming the willingness of their publics to sustain the large costs of an indefinite occupation, will never be able to provide stability in the parts of Syria and Iraq they occupy. Only the locals, with suitable political will, can do that. A huge unanswered question about notions of taking out ISIS with military force is what fills the void once it has been taken out—what, that is, other than an indefinite and costly foreign occupation. That question will have a satisfying answer only when peace-making diplomacy and political reconciliation have made much more progress than they have so far. Until that happens, the place of a taken-out ISIS will be taken by more of the conflict and chaos that violent extremists, whether they bear the ISIS name or some other label, are best able to exploit.