Why should the United States care about Syria?
A lot of people are dying in a terrible conflict that shows no signs of abating. Syria is surrounded by U.S. allies - Israel, Jordan and Turkey - which are all affected by the war. It threatens to spread instability, sectarian conflict and political competition in a part of the world that has plenty of all three. Syria is a crucial ally for Iran, which means the war has big implications for Iran's foreign policy and its tenuous relationship with much of the world. The war is a growing haven for Islamist extremists, including groups allied with al-Qaida.
The question of what the United States should do about Syria, if anything, is also a proxy for larger questions about America's role in the world and its willingness to use force. It touches on the legacy of the Iraq war, but also on how the United States deals with international institutions and humanitarian crises abroad.
Syria is a catastrophe. What does the United States stand to gain by getting involved?
The Obama administration's primary case is that the United States has a responsibility, as a global leader, to punish Syrian President Bashar Assad for using chemical weapons. The world has a fragile and hard-earned understanding that chemical weapons are not used in wars, no matter how brutal. If the United States (or any other nation) doesn't rebuke Assad, the global stand against chemical weapons will be weakened, opening the door to possible use of chemical weapons in the future. Preventing that would be good for the United States, because we don't want to live in a world where people use chemical weapons and because we want to continue to be perceived as a global leader.
The administration also argues that the United States needs to protect its "credibility." Obama had earlier called chemical weapons a "red line"; if he doesn't respond to that line being crossed, some worry that foreign leaders might take U.S. threats less seriously in the future. The administration also says the United States has immediate national security interests in mitigating Syria's war, which threatens to spread into neighboring countries, although the strikes would be less about containment and more about deterring the use of chemical weapons.
What does the United States have to lose by launching strikes?
It's possible that strikes won't actually deter Assad from using chemical weapons and could even make him more likely to use them if he panics. Strikes could also inflame anti-Americanism in Syria or the region. And cruise missiles could kill innocent civilians.
The biggest concern, though, is that the United States could get sucked into a war it has worked hard to avoid. Mission creep happened after the United States invaded Iraq and Afghanistan; it also happened in Libya in 2011, when a "no-fly zone" grew into an all-out intervention against Moammar Gadhafi. The danger that limited strikes will become something more open-ended is real.
What if Syria or its allies strike back?
The Syrian military does not have much capability to strike back. More to the point, it's not as interested. Assad doesn't want to escalate a conflict against the most powerful military on the planet.
Although it's possible that he or an ally could launch a symbolic retaliation, Assad's interests are best served by taking his lumps and moving on.
Should we try to do something bigger that might end the war?
That's what some lawmakers, particularly Republican Sens. John McCain, Ariz., and Lindsey O. Graham, S.C., have been advocating. They say the United States should take stronger military action in support of the rebels to topple Assad. They argue that the war is only going to get worse if we don't.
The war sprawls across many front lines and sectarian divides. Analysts disagree about what it would take to defeat Assad's forces, but at the very least it would require heavy support to rebel groups, which are disorganized and often tied to anti-American extremists.
The more difficult question is what happens after Assad is defeated. One lesson that the United States learned in Iraq: It's difficult to keep armed adversaries from killing each other. Tamping down Iraq's sectarian violence required a massive commitment of ground troops over several years, but it's not clear that the mission succeeded.
Who is better for the United States, Assad or the rebels?
Neither is good for American interests. Assad, in addition to being an oppressive dictator at home, is an anti-American leader who supports Iran and the Lebanese militant group Hezbollah. But at least he had been predictable.
There's a growing fear that the rebels could be worse. Some groups say they want democracy, but some openly espouse allegiance to al-Qaida and are already imposing a severe form of ultraconservative Islamist rule in areas they control. It's not clear who would come out on top, but political vacuums tend to empower extremists.
The United States has already seen this movie in Afghanistan, where after an amalgam of rebel groups forced out the Soviet-backed puppet government, infighting among them led to civil war and ultimately Taliban rule. Perversely, the best way to keep this from happening in Syria is for the Assad government to retain at least some power.
How would strikes affect U.S. relations with the Arab world?
It sure wouldn't help. Although some Arab governments support strikes, Arab people tend to be deeply uncomfortable with the idea of Western military intervention in their region.
The first Gulf War, in which a U.S.-led force expelled Iraqi troops from Kuwait in 1990 and 1991, inspired pro-Saddam Hussein protests across much of the Arab world, even though Saddam Hussein was not particularly beloved. And the scars of the U.S.-led 2003 invasion of Iraq have not healed. U.S. strikes on another Arab country, even if meant to ameliorate the war, are not going to help America's already-troubled image in the region.
How would strikes affect U.S. relations with Russia and Iran?
If you support confrontational approaches to Russia and Iran, Syria's two main allies, airstrikes on Syria probably make some sense to you. Crippling Assad would weaken them, too, and send a message to Iran that the United States is willing to use force to deter the use of chemical weapons.
If you support engagement with Moscow and the effort to build better relations with Iran, whose new president, Hassan Rouhani, has indicated an interest in diplomacy, airstrikes would be a setback. Launching missiles into Syria would put Iran in more of a defensive crouch; it could also make it tougher for Rouhani to bring more hard-line Iranians on board for diplomatic talks.
Some people say a political solution would be better. Shouldn't we try that?
That has been the Obama administration's policy all along: encouraging Assad and the rebels to negotiate a peace deal. It would avoid the chaos of a political vacuum and could be the best way to end sectarian fighting. But it hasn't gone anywhere in two years, first because the Assad government didn't want to negotiate and now because the rebels are too fractured to present a united front at the negotiating table.
A political solution would leave a portion of the Assad government in power, which is disagreeable for obvious reasons. Some analysts argue that strikes could help force the Assad government to negotiate a peace deal. The model here is the 1995 Dayton Accords, when NATO-led bombings in Bosnia helped force the government to enter peace talks.
What happens if we do nothing?
The likely outcomes of inaction don't look so different from the likely outcomes to limited strikes. After two-plus years of deeply entrenched civil war, not to mention active meddling from such regional powers as Iran and Saudi Arabia, Syria is being shaped by forces far more powerful than a few American cruise missiles. The fighting has taken on a self-perpetuating velocity that would be difficult to stop.
The biggest risks of inaction for the United States are that the taboo against using chemical weapons would become a bit weaker, especially within Syria, and that the United States would be perceived as further losing some of its international primacy. After setbacks in Egypt and tension with Saudi Arabia over the region's future, the United States would see its influence in the region take another hit.
The biggest upside of inaction for the United States would be to avoid getting sucked into a terrible conflict with no obvious solution or end in sight.
Would voting down the president's request hurt U.S. foreign policy?
Analysts tend to make this argument when they think Congress is about to block the president from doing something they see as worthwhile in foreign policy.
In 2010, when it looked like the Senate would refuse to ratify a nuclear arms reduction treaty that Obama had negotiated with Russia, a number of left-leaning analysts said that this would hurt U.S. credibility abroad by hobbling the president's ability to deliver on promises he makes to foreign leaders.
Plenty of right-leaning analysts warned the same thing when George W. Bush's foreign policy was challenged by a Democratic Congress after 2006.
The truth is probably that the American political process is not well understood in foreign capitals, just as Washington can often misread how Moscow or Beijing or Tehran make decisions. The United States, like any other country, is judged more on action than on rhetoric.