blundering of Obama.
Ever since the civil war in Syria started there have been legions of progressive and neo-conservative commentators calling on Obama to act in the aid of the rebels. Those arguments have invariably been of the humanitarian persuasion rather than the geopolitical due to one important fact. While Assad is a dictator and an enemy of the United States, and the deaths of thousands of innocent civilians are heart wrenching, the fact is that there is little reason for the United States to get involved in the conflict.
Ordinarily the United States might involve itself in a civil war like this. The Syrian government essentially acts as a proxy for one of our rivals in the Middle East, Iran, and what better way to weaken our rival than replace one of their proxies with one of our own. This time, however, the rebelling faction is largely, if not entirely, aligned with another enemy of ours, the Islamists. Even though the deaths of innocents are appalling, the regime in charge is evil and that the conflict posses a great deal of risk for two of our allies in the region, Israel and Turkey, there is little upside in our involvement. The status quo is the best situation that exists for the United States geopoliticaly. We have two enemies killing each other, weakening each other, all with out the United States having to involve itself. This isn't to say that this is an ideal situation, it isn't, or that the United States prefers whats going on, it doesn't, but there is little real incentive to do anything other than watch. Provided that our political leaders don't make a reason. That is just what Obama did.
Obama declared a red line because he wanted to appease all the interventionists, specfically the humanitarian interventionalists, without actually doing anything of consequence. Threats like this are potentially good PR for the president. He can appear tougher on Assad without actually having to be tougher, which entails the risk supporting some of America's enemies, and at the same time can claim credit if Assad doesn't use chemical weapons. Politicans and world leaders bluff all the time, except this time, it was called. Whether or not it was Assad, the rebels, or some third party, it doesn't really matter in the geopolitical perspective. What matters is that a line was drawn and someone stepped over it.
By Obama declaring the red line he created parameters that the United States would be obligated, morally at least, to involve itself. Furthermore, he also created a situation where he risked America's soft power, whether he realized it or not. What I mean by soft power is that ephemeral power that politicians and diplomats put so much credence in. Soft power is essentially reputation and the ability to get things done with that reputation. The United States can make a nation do what it wants via hard power, the military or economy, but it is easier, less costly and more public relations friendly to use soft power. Veiled threats constitute soft power of sorts, the unspoken warning implied by a 'red line' for example, and the major nations of the world pay attention to it.
Russia, America and China all make policy decisions based on what they think their rivals will do. If they think a certain ask carries the real risk of retaliation, then they are less likely to undertake a particular action. This explains why America doesn't revok favored nation status for China despite their merchantilism, or that China doesn't call the debt due when America conducts military exercises with the South Korans in the North China sea. Doing so carries real risk of retaliation.
Now, if the United States doesn't act it looks weak in front of her rivals and allies, and soft power is severely diminished when a nation looks weak. If the United States doesn't act it now it risks helping the very enemies that we have been fighting, pretty succesfully, to contain. Perhaps even worse, is that if the US will react military it will have to act far more hastily than it would have wanted. The cries from the humanitarians are now harder to ignore and America's rivals are waiting to see what she does. Because Obama's political posturing in the geopolitical arena the United States has now lost their best option, sit and do nothing. Before the United States could opt to take a wait and see approach and not risk diminishing it's soft power. She wouldn't look weak to her rivals and no promises were made. Now both options are in play.