The possibility that the Obama administration is considering supplying military assistance directly to Sunni tribes in Anbar underscores a central challenge in Washington’s approach to Iraq, Syria, and the Middle East generally. I call it the “one person’s floor is another person’s ceiling” problem.

That the floor below you can also serve as somebody else’s ceiling means a pretty close connection in a variety of situations, whether noise issues or leaky pipes or a thin divide separating two parties. Now consider how U.S. actions in a region where things are often interconnected and where policy initiatives can have consequences–often unintended–on other parties.