I was asked by the readers of the new website The Question to name the greatest failure of President Obama as he prepares to leave office after eight years.

Syria. Let’s recognise the magnitude of what we’re talking about here. Half a million dead in 5 1/2 years. Eleven million displaced or refugees. It’s not just the magnitude of that; it becomes a focal case that everybody watches, that everybody looks at. Vietnam was not just a failure back in the 1960s and 70s because America was defeated – it was what Vietnam symbolized for American power around the world for many decades afterwards. So Syria becomes a symbolic failure of American power and American values for decades to come.

As a President, you can anticipate the way things go. It isn’t the case that Syria completely caught Obama by surprise. If things go completely pear-shaped in a country, as President you either have to say, “We’re standing aside from this, however bad it gets for the people there,” or you can say, “We will not tolerate a leader mass-murdering his people.”

What Obama said, in 2011, was “We will not tolerate a leader mass-murdering his people.” We remember the “red line” on chemical attacks, but there was also a red line on mass murder – and Assad had started doing precisely that, well before the chemical attacks.

Obama had put himself in a position where you either back that up, and at least protect some of these people, or you stand aside. If Obama had said at this point, “You know what? This is just too difficult. We just can’t protect these people,” it’s a horrible decision, but it’s there. But what he continued to do was give the public the idea that Assad was terrible, while blocking any effective action.

That’s why August 2013 is such a marker – it’s not just the numbers of deaths, but the fact that Assad used chemical weapons. Obama had said we were going to protect these people, and then he U-turns and walks away from them.