Back when he was just a U.S. senator, Barack Obama used to say that he didn't oppose all wars, just "dumb wars." I assumed that by "dumb wars," he meant wars to address phantom or exaggerated threats (see: Iraq, 2003), or wars launched to achieve domestic political objectives (see also: Iraq, 2003), or wars begun without sufficient attention to alternatives, capabilities or strategic consequences (see yet again: Iraq, 2003).

Apparently, I was wrong: All Obama really meant was that he opposed long, expensive, politically unpopular wars involving lots of American ground forces and lots of American casualties. He's fine with other kinds of dumb wars (though he prefers to avoid the W-word, and instead uses phrases like "military action" and "targeted strikes.")

But call it what you will: I have a sinking feeling that what the United States is about to do in Syria may turn out to be another dumb war.

How is it dumb? Let me count the ways. First: the Islamic State in Iraq and the Levant (ISIL) is an undeniably nasty group, but even the president admits that ISIL poses no immediate threat to the United States. Second, other actors may be better suited than the United States to combating the regional threat ISIL poses. Third, U.S. military strikes against ISIL in Syria risk inspiring more new violent extremists than they kill, undermining long-term U.S. security interests. Fourth, our current fixation on ISIL also carries opportunity costs. Fifth, Obama's willingness to embrace and expand George W. Bush's doctrine of unilateral preventive self-defense is one more nail in the coffin of the fragile post-World War II collective security system.

Dumb, Part I: Threat inflation

According to the latest Washington Post poll, 59 percent of Americans think that ISIL poses a "very serious threat to the vital interests of the United States." They didn't think this a few weeks ago, but televised beheadings have a way of capturing public attention.

Nonetheless, two tragic and gruesome beheadings do not an existential threat create. (If beheadings were a sufficient casus belli, we should consider airstrikes against violent Mexican drug cartels, several of which appear to specialize in decapitations. And unlike ISIL, the cartels — which have killed tens of thousands of people in the last few years — already have a major presence inside the United States.)

ISIL is plenty brutal, but most experts say it is neither as well-organized nor as sophisticated as Al-Qaida was before 9/11. Most estimates suggest it has no more than 20,000 fighters, many of them inexperienced; Obama admits that there is no evidence that it has cells in the United States or has the ability to stage attacks inside the United States.

Though some Americans have reportedly joined ISIL fighters in Syria, the number is apparently quite small. Hypothetically, it's always possible that a few of those Americans will eventually return to the U.S. and try to plan attacks here, but as the Boston Marathon bombing made clear, alienated young men bent on killing people in the U.S. don't need to go off and train in foreign lands. Why bother, when they can find Al-Qaida bomb-making recipes right there on the Internet?

In any case, when it comes to homegrown violent extremism, jihadist sympathizers have nothing on old-fashioned right-wing crazies: According to data compiled by the New America Foundation, homegrown jihadists have killed only 21 people (13 of whom were victims of the Fort Hood massacre) in the 13 years since 9/11, while right-wing extremists accounted for 37 victims.

ISIL is a direct threat to the regime of Syria's Bashar Assad, but since Assad's forces have so far killed scores of thousands more people than ISIL, it's hard to feel too sorry for him. ISIL is also a threat to rival Islamist rebel groups inside Syria, including groups directly tied to Al-Qaida. Why not let them all slug it out, on the theory that the brutality of all concerned will ultimately do more to discredit jihadist violence than anything the United States could possible say or do?

Granted, letting them all slug it out is surely a threat to Syria's beleaguered civilian population — but since the White House has been willing to watch Syria's civilians suffer for three years now, we can probably conclude that protecting Syrian civilians has never been considered a vital U.S. interest.

ISIL is also a threat to Iraq's increasingly nominal central government, but here again, this doesn't necessarily make it a threat to a core U.S. interest. While the group has ample capacity to cause mayhem — and its rapid advance into Iraq revealed the hollowness of portions of the Iraqi Army — there is little reason to believe it has the ability to hold and control the territory it has seized. As American troops learned many times over the last 13 years, it's one thing to seize territory; holding and building is another thing altogether. Iraq's remaining armed forces greatly outnumber ISIL's small band of fighters; with intelligence, planning and logistics assistance from U.S. military advisers, they stand a decent chance of turning the tide against ISIL without the aid of additional U.S. strikes in Syria.

At the risk of being heretical, it's not clear that vital U.S. interests are threatened even if ISIL does succeed in holding the territory it has gained inside Iraq. If Iraq ends up in a state of de facto sectarian and ethnic partition — which Vice President Joe Biden once advocated as the only route to enduring stability — it's not the worst outcome. It's not a good outcome — but as Otto von Bismarck, Germany's first chancellor, famously said, "politics is the art of the possible, the attainable — the art of the next best."

ISIL was able to roll through parts of Iraq in large part because Sunni tribes, alienated by former Prime Minister Nouri al-Maliki's divisive policies, were willing to form an alliance of convenience with the new fighters in town. Many analysts say those Sunni tribes won't hesitate to dispense with ISIL once the group ceases to be so convenient. Arguably, a partitioned Iraq would be more stable than a nonpartitioned Iraq — and past events demonstrate that Iraq's Sunni tribes are capable of working pragmatically with the United States when it's in their interest to do so.

Dumb, Part II: Believing this problem requires an American solution

Assad, the Al Nusra Front and the Iraqi government aren't the only actors dismayed by ISIL's advances. Our Iranian adversaries — who provide substantial backing to the Shiite-dominated Iraqi government, as well as to private Shiite militias, and who have also been supporting the Assad regime in Syria — are appalled by ISIL's progress. Meanwhile, our frenemies the Saudis, who even more fond of beheadings than ISIL, nonetheless recognize ISIL as a profoundly destabilizing force. Ditto for the Jordanians, the Kurds and the Turks.

Obama says the United States will "lead" a coalition against ISIL, but the United States should instead step back and let other regional actors assume the lead. They have a strong incentive to combat ISIL (an incentive we undermine when we offer to do the job for them), and the common threat of ISIL may even help lead to slightly less chilly relations between Iran and Saudi Arabia (though I won't hold my breath).

Other Middle East powers also have greater ability than we do to understand local dynamics, not least of which because many share a common language with ISIL or with other actors in the mix. The Kurds and the Jordanians may need some U.S. help to protect their own territory, and other states may need intelligence or other forms of logistical assistance. But we can provide such support to any of our allies and partners without putting ourselves front and center in the effort to combat ISIL.

Dumb, Part III: Believing that standoff strikes will eliminate the threat

Airstrikes are an excellent way to turn live people into dead people, and the United States has an impressive ability to carry them out with minimal damage to unintended targets. But airstrikes are a very poor way to hold territory, and an even worse way to establish stable and legitimate governance structures. Without capable partners on the ground in Syria, it's not clear that U.S. airstrikes against ISIL will achieve the objectives we want to achieve — though anything that hurts ISIL will surely gladden the twisted little hearts of Assad and leaders of rival extremist groups.

It would be really nice, just about now, to have some well-armed, well-led, realio-trulio moderate Syrian rebels with whom we could coordinate — but I think we missed that boat a long time ago. Today, rebels who are both moderate and good at fighting are about as common in Syria as pink fluffy unicorns.

Standoff airstrikes also have an unfortunate tendency to make people mad. Drones, in particular, have become a divisive symbol of American power — of our fearsome ability to kill without assuming any immediate risk to ourselves. Standoff strikes may succeed in degrading ISIL's near-term ability to be an effective fighting force, but there's a real, if non-quantifiable, risk that U.S. strikes will ultimately inspire even more disaffected young men to join violent jihadist groups.

Since taking office, President Obama has relied increasingly on drone strikes to counter terrorist threats. A couple thousand dead bad guys later, the global terrorist threat has merely metamorphosed, and in many ways it appears to be as bad as ever.

Why do we think a counterterrorism approach that had achieved no strategic success so far will suddenly start working in Syria?

ISIL is far from invincible, but if we were truly serious about degrading or destroying ISIL in Syria, we'd need to cross John Kerry's latest red line and put some American boots on the ground. Not 100,000 boots — a fairly small number of American special operators working with the few remaining local unicorns might even do the trick — but boots nonetheless. That would be risky, of course; some of those Americans might get killed. But if ISIL is truly a threat to core U.S. interests, it's a risk we should be willing to take.

The administration's unwillingness to put U.S. troops on the ground in Syria sends an all-too clear message both to Americans and to the rest of the world: Actually, destroying ISIL isn't that important to us. Combating ISIL is just important enough that we need to demonstrate that we're "doing something" — but not quite important enough for us to bother to do it right.

Dumb, Part IV: Chasing the soccer ball

The U.S. security establishment loves to chase en masse after the threat du jour. (Yes! I speak French, the language of diplomacy.) Once, the threat was Al-Qaida and the Taliban; today, it's ISIL.

But as we pour money and energy into combating ISIL, we risk overlooking other threats and opportunities. Is ISIL truly more dangerous to the United States than violent Mexican drug cartels, or the pro-Russian Ukrainian rebels who brought down a passenger jet with an anti-aircraft missile in July, or the long-term effects of climate change? Shouldn't we spare a few brain cells (and a few bucks) for all that other stuff?

Dumb, Part V: Setting bad legal precedents

Last, but not least, the president's decision to authorize airstrikes in Syria risks cementing a dangerous legal precedent — and I'm not even talking about his decision to bypass Congress. Since World War II, the U.N. Charter's rules on the use of force have helped substantially reduce interstate conflict, but Obama's speech last week just tossed those international law rules out the window.

The basic idea of the U.N. Charter system is that unless they have Security Council authorization, states can't use force inside other sovereign states without their consent. The only exception is the use of force in self-defense. Traditionally, self-defense has been understood narrowly: it permits force to be used to prevent an imminent attack, but not against actors who don't pose any immediate threat.

Unless we plan to ask Assad for his blessing first, it's not clear that the United States has any basis under international law to use force against ISIL inside Syria's borders Obama acknowledges that the United States has detected no "specific plotting against our homeland." Instead, he falls back on speculative hypotheticals: "If left unchecked, these terrorists could pose a growing threat beyond that region, including to the United States," and Westerners who join ISIL "could try to return to their home countries and carry out deadly attacks."

The Bush administration invoked the idea of preventive self-defense to justify the 2003 invasion of Iraq: "If we wait for threats to fully materialize, we will have waited too long." But in his 2007 book, The Audacity of Hope, Sen. Obama rightly rejected this approach. The United States has "the right to take unilateral military action to eliminate an imminent threat to our security," he wrote, but only "so long as an imminent threat is understood to be a nation, group, or individual that is actively preparing to strike U.S. targets." This would seem to rule out military action against a group that has no specific plan to strike the United States but merely "could" pose a "growing" threat sometime in the unspecified future.

America's words and actions are precedent-setting. If we flout international law restrictions on the use of force, we'd better be prepared for the precedents we're setting to come back and bite us.

Stop laughing, Vladimir Putin. It's not very polite.

Dumb, Part the Last: Forgetting the most important question

Tell me how this ends?

I don't envy President Obama. The challenges posed by the rise of ISIL are complex and difficult, and the politics are extraordinarily tangled. But it all reminds me of a famous line from Oliver Wendell Holmes Jr., who served on the Supreme Court a century ago: "Hard cases make bad law."

In foreign policy, hard cases make dumb wars.

Rosa Brooks is a law professor at Georgetown University and a fellow at the New America Foundation. She served as a counselor to the U.S. undersecretary of defense for policy from 2009 to 2011 and previously served as a State Department senior adviser.