1) Politics doesn't actually stop at the water's edge. There's an old adage that "politics stops at the water's edge" — that is, lawmakers usually set aside partisanship when debating war. This turns out not to be true. Sarah Binder points to an old essay by William G. Howell and Jon C. Pevehouse arguing that partisanship has historically played a very large role in these debates.
To wit: "When the opposition party holds a large number of seats or controls one or both chambers of Congress, members routinely challenge the president and step up oversight of foreign conflicts; when the legislative branch is dominated by the president’s party, it generally goes along with the White House."
2) Presidents rarely feel constrained by Congress on war matters. Over at the Monkey Cage, Andrew Rudalevige of Bowdoin has been writing an informative series of posts on the War Powers Resolution, the 1973 law that, in theory, requires the president to get the consent of Congress before committing to an armed conflict.
Most presidents have never formally invoked the resolution — the one exception was Gerald Ford in 1975. Occasionally presidents have sought congressional approval for military action, but they've usually insisted that they don't need to. (Congress authorized the Gulf War in 1991, but George H.W. Bush maintained that "I didn’t have to get permission from some old goat in Congress to kick Saddam Hussein out of Kuwait.”)
And Rudalevige argues that this dynamic isn't likely to change too significantly in the future — even though President Obama has asked Congress to weigh in on Syria. "The combination of circumstances it entails seems rare in the annals of presidential uses of force," he notes.
3) Elite opinion on war plays a huge role in shaping public opinion. Intervention in Syria is pretty unpopular with the wider American public right now. But it won't necessarily stay that way. A lot could depend on the words and actions of lawmakers and other elites.
At least, that's one implication of a 2007 paper by Adam Berinsky of MIT: "When political elites disagree as to the wisdom of intervention, the public divides as well. But when elites come to a common interpretation of a political reality, the public gives them great latitude to wage war.” (See also Berinsky's book on this topic.)
4) Broadly speaking, military interventions have a poor track record in achieving humanitarian goals. True, the Obama administration isn't framing a strike on Syria as a humanitarian endeavor (their stated goal is to enforce norms against the use of chemical weapons). Still, Erica Chenoweth of the University of Denver has been highlighting a couple of striking papers on the consequences of intervention:
--A 2002 paper by Patrick Ragan found that outside military interventions don't typically shorten the duration of civil conflicts. "Regardless of how the intervention is conceived – or empirically operationalized—there seems to be no mix of strategies that lead to shorter expected durations."
--A 2012 paper by Reed Wood, Jason Kathman and Stephen Gent found that outside military interventions on behalf of rebel factions can actually increase government killings of civilians:
A separate 2012 study by Dursun Peksen, meanwhile, found that hostile interventions by outside powers against a country's government tend to "increase the probability of political imprisonment while having no major effect on extrajudicial killing, disappearance, and torture."
5) Not all military interventions are the same. Over at Duck of Minerva, Jon Western raised an obvious objection to the papers Chenoweth cited. Not all military interventions are alike. Some have been disastrously bad at curbing violence. Others, he argues, seem to be more effective. "The question then is — what are the informative cases for Syria?" he asks. "Is it closer to the Balkans or to Iraq and Afghanistan?"
Chenoweth replies that, based on her read of the research, the sort of interventions most effective at curtailing violence seem to be multilateral peacekeeping missions that occur when the combatants are already ready to negotiate. If those conditions are absent, she argues, "the outcomes of international intervention are much less favorable in both strategic and humanitarian terms."
Georgetown's Erik Voeten, meanwhile, wonders if Syria is simply too different from past conflicts to draw any firm conclusions from this research: "My main point is that I cannot think of many or even any comparable cases to Syria: where the intervention is a limited bombing campaign that takes place after the mass killing has long been under way."
6) In foreign policy, "credibility" is often overrated. One argument often cited in favor of U.S. military intervention is that U.S. credibility is on the line — i.e., that it would be disastrous if Assad could violate Obama's "red line" on chemical weapons with impunity.
But in a Foreign Affairs essay, the University of Washington's Jonathan Mercer cites "broad and deep evidence" that credibility in foreign affairs is a bit of a myth. One example: "Ted Hopf, a professor of political science at the National University of Singapore, has found that the Soviet Union did not think the United States was irresolute for abandoning Vietnam."
7) The legal questions around Syria's alleged chemical weapon use are much trickier than they seem. Northwestern's Ian Hurd points out that Syria isn't a party to the Chemical Weapons Convention of 1993. That means even if the Syrian government did, in fact, use chemical weapons, "as a legal matter, [that] does not automatically justify armed intervention by the United States."
Charli Carpenter of UMass Amherst disagrees somewhat, arguing that Syria would have violated clear international norms if the government had used chemical weapons. But she agrees that a U.S. attack on Syria would still be hard to justify under international law: "If Western powers led the attack without the Security Council or the General Assembly, it is hard to argue that it would be legal — regardless of what Syria has done inside its borders."
"If the goal is to affirm international norms," Carpenter concludes, "the far better way to frame a potential military strike is in terms of ethics and norms, not law."