Eliot A Cohen, writing in the Wall Street Journal:
[A]s a practical matter, critics can ask why the U.S. should intervene after a massacre, however hideous, of some 1,400 Syrians, when America has refused to act over the slaughter of 100,000 in the preceding two years. And, even if the U.S. strikes at Assad and helps bring about his downfall, the danger is real that having administered a defeat to the regime and its sponsor, Iran, America will hand a victory to al Qaeda.
These are all serious arguments. But weightier are the counterarguments. For better or for worse, the credibility not only of this president, but of America as a global power and a guarantor of international order, is on the line. If the U.S.—after its president said two years ago that Assad must go and then, a year later, drew a red line at Syria's use of chemical weapons—now does nothing, profound conclusions will be drawn by a China ready to bully its neighbors, by a North Korea whose scruples are already minimal, and by an Iran that has already killed many Americans in a covert war waged against us in Iraq and Afghanistan.
America's friends will realize that its word means nothing. As a result, they will either abandon us, or arm themselves with nuclear weapons. And these countries will be increasingly willing to wield them in a world in which they have no great ally who may be counted upon to stand by them in an hour of need.
One has to suspect that the Syrian government deliberately used sarin in the Damascus suburbs while United Nations inspectors were in the capital, and on the eve of the anniversary of Mr. Obama's red line statement. The essence of tyranny is this message to a population: "We will impose our will on you. No one cares about your suffering, and no one will do anything to rescue you." Assad's message was delivered by chemical weapons of mass destruction. Civilized nations let that message remain unanswered at their peril.
Whole thing here.