The original rationale for the Iraq War was that the U.S. wasn’t safe so long as Saddam Hussein had weapons of mass destruction. It quickly became clear that wasn’t enough to justify an invasion. So other arguments were trotted out — each suggesting more ambitious goals, and thus requiring more expansive means, than the last. Hussein was a murderous dictator and freeing his people from brutality was the moral thing to do; Hussein’s WMDs were inspiring Iran’s weapons pursuit, and removing them would help end the region’s arms race; Iraq could be transformed into a secular liberal democracy that would stand as a shining counterexample to Islamic authoritarians throughout the Middle East.

Some reasons had nothing to do with Iraq at all. Many Americans simply wanted revenge for the Sept. 11 attacks, and they’d been convinced, wrongly, that Hussein had something to do with al-Qaeda’s plot. Some elites also wanted revenge for the attacks even though they knew Hussein had nothing to do with them. “Afghanistan wasn’t enough,” Henry Kissinger is reported to have told speechwriter Michael Gerson. “We need to humiliate them.”

The Iraq War was, at the start, all things to all hawks. It had to be. Otherwise the George W. Bush administration could never have mustered enough support to enter Iraq in the first place.

The arguments for striking Iraq were ultimately catastrophic: Americans were not prepared for the war they got. The arguments for striking Syria are generally narrower and better founded. But after speaking with a number of supporters, it’s clear their rationales are, nevertheless, numerous — and occasionally contradictory. Here is a survey of the most common.

1. Punish Bashar al-Assad for using chemical weapons.

The argument: Assad used chemical weapons on the Syrian people, contravening international norms and crossing President Barack Obama’s red line. If nothing is done in response, Assad will continue using chemical weapons. Assad “has barely put a dent in his enormous stockpile,” said Samantha Power, U.S. ambassador to the United Nations. “And the international community has clearly not yet put a dent in his willingness to use them.” Bombing his military infrastructure would deliver that dent.

The counterargument: “If we go in with a surgical strike and the regime survives, is that really punishment?” asks Republican Senator James Risch of Idaho. “Who’s going to get punished? The people or the regime? What happens on the day we’re done and he crawls out of his hole and stands up and says, ‘That all you’ve got?’ What have we done to our reputation or the confidence people have in our military? I could make a case that that’s a worse situation than if you do nothing.”

Risch’s scenario can be taken further. What if we strike and then Assad uses chemical weapons again? Or simply increases his slaughter of civilians using conventional weapons? Are we open to intervening more aggressively?

Achievability: High. We can definitely bomb Assad until it hurts. The question is what happens after he’s hurt.

2. Deter future dictators from using chemical weapons.

The argument: The ban on chemical weapons use has worked extraordinarily well since World War II. That’s meant fewer civilian deaths and fewer chemical weapons around to fall into the hands of terrorists or rogue states. The ban is worth preserving, and bombing Assad will help preserve it. “The goal here is to deter dictators in 2022 from using chemical weapons on a mass scale against civilians,” said Democratic Representative Brad Sherman of California.

The counterargument: The ban will continue working even if Assad goes unpunished. After all, Iraq’s use of chemical weapons against Iran in 1988 went unpunished, yet there was no explosion in chemical weapons use around the world. Syria is one of only a handful of countries that have refused to sign the international ban on chemical weapons; there’s simply no evidence other nations are aching to join that club.

Achievability: Low. A dictator facing regime collapse in 2030 isn’t going to care how Obama handled Assad in 2013. He might care what the U.S. president in 2030 is likely to do (or perhaps what the Chinese premier is likely to do). The 2013 precedent might be more powerful if the U.S. had backing from the UN Security Council, in which case strikes would reinforce the international community’s willingness to punish transgressions. But so long as the U.S. is going solo, it’s unlikely any lesson will outlast Obama’s presidency.

3. Deter Iran from obtaining nuclear weapons.

The argument: If Obama can’t obtain congressional authorization for limited strikes against Syria, Iranian leaders will be emboldened to accelerate their nuclear weapons program, knowing full well that the U.S. has proved itself a paper tiger. Only by striking Syria can the U.S. show that it takes weapons of mass destruction seriously and has the resolve to act against them.

The counterargument: First, the strategy might backfire. Iranians might interpret strikes against Syria as evidence that they need to accelerate their nuclear program to defend against U.S. attack. Second, that game is already over. Even if Obama manages to obtain congressional authorization for a Syria strike, Iran has already witnessed just how war weary the American public is — even for a limited fight against a weak enemy with little chance of U.S. casualties. Finally, Iran’s leaders understand that if the U.S. doesn’t act to stop their weapons program, Israel might — and, when push comes to shove, the U.S. will back Israel.

Achievability: Low. There’s just too much uncertainty, and attacking Iran to disrupt their pursuit of nuclear weapons is a terrible idea anyway.

4. Force Assad to the negotiating table.

The argument: There are three ways U.S. strikes could weaken Assad’s position. First, by directly damaging his military capabilities: The targets would be military installations, infrastructure and communications.

Second, by convincing Assad that the cost of deploying chemical weapons is too high, causing him to lose a tactical advantage over the insurgency.

Third, by giving the insurgents a psychological boost and, through the McCain-Coons amendment, which expressly calls for changing “momentum” in the war and ultimately for the installation of a democratic government, a financial and strategic boost, as well. All that might lead Assad to believe he can’t win the war outright, and that he’s better off negotiating a clean end than taking the chance he’ll be executed by the next regime.

The counterargument: This goal contradicts the administration’s stated intention to limit strikes so they don’t drastically disrupt the balance of power in the civil war. An “unbelievably small” war, to use Secretary of State John Kerry’s odd turn of phrase, is not a war likely to force Assad to do anything.

The Obama administration seems to think that it can use the blunt instruments of cruise missiles with incredible precision. But calibrating strikes so that they’re powerful enough to drive Assad to the negotiating table but not so devastating that they enable his opponents to seize the initiative and take control of Syria is probably an impossible task. Either the strikes seriously hurt Assad — and then what do we do? — or they will be too limited to alter Assad’s incentives to negotiate.

Achievability: Middling. Hitting Assad hard enough to force him to negotiate or lose control is certainly possible. But it risks deeper U.S. involvement in the civil war — or in the chaos that follows. And no one seems to want that.

5. Stop the bloodshed.

The argument: Syria is a humanitarian tragedy — and not just because of chemical weapons. “Remember the Boston Massacre of 1770 from our history books, in which five people were killed?” asked Nicholas Kristof in the New York Times. “Syria loses that many people every 45 minutes on average, around the clock.”

Kristof wrote: “If we were fighting against an incomparably harsher dictator using chemical weapons on our own neighborhoods, and dropping napalm-like substances on our children’s schools, would we regard other countries as ‘pro-peace’ if they sat on the fence as our dead piled up?”

The counterargument: Yes, Syria is a tragedy. But it’s not as bad as the Democratic Republic of Congo’s never-ending conflict. And if the goal is saving lives, we could do more good by fighting malaria. Awful deaths and mounting casualty tolls are insufficient to enlist the American people in someone else’s civil war, or even, quite often, to spur them to commit financial aid.

If Obama were to ask Congress to authorize humanitarian intervention in Syria, he’d lose the vote overwhelmingly. Instead, the administration has defined the U.S. interest, somewhat perversely, as encouraging Assad to forgo chemical weapons and proceed with slaughtering his people only with conventional incendiary devices.

Achievability: Extremely low. It’s not even clear what humanitarian intervention in Syria means. Toppling Assad would devolve power to a brutal and fractured opposition, with Assad’s large stores of chemical weapons falling into the hands of god-knows-who. The U.S. would be forced to navigate a world of revenge killings and reprisals as Assad’s army, backed by his Alawite sect, evolved into an insurgency. And that’s assuming the U.S. possessed the stomach for such an intervention, and the inevitable deaths of U.S. soldiers — which it doesn’t.

The arguments for intervening in Syria seem to fit a frustrating pattern: What’s achievable isn’t that valuable, and what’s valuable isn’t achievable. We could punish Assad and make good on Obama’s red-line rhetoric, but those payoffs seem paltry given the risks of intervening in another complicated Middle East conflict. Conversely, ending the bloodshed would be a tremendous act of heroism and decency, but not one we seem capable of pulling off.

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Ezra Klein

Follow Ezra on Twitter @ezraklein. Ezra Klein is the founder and editor-in-chief of