1. Don't make threats or tie yourself down, unless you're sure you can and will follow through. And even then, do your best not to make threats; keep your options open.
2. Don't listen to exile groups or rebel leaders. They may be brave, patriotic and even great. But they are also, almost by definition, opportunists and liars, eager to drag great powers into conflicts that have little or nothing to do with their own interests. Journalists only amplify this.
3. The people who talk most about international law and norms are mainly self-appointed groups with no actual constituencies who navigate and lobby elite global opinion, often with very benign motives and sometimes with benign effects.
4. Whether the US attacks Damascus or does not attack Damascus won't have much effect on whether the US can in the future, under whatever circumstances, threaten or use force wherever else it wants to, to buttress or enforce whatever other international norm it chooses to. The entire concept of 'unitary credibility' is flawed to its core.
5. Most of these world policing conundrums come down to the imbalance of power and accountability in the international state system.