Inevitably enough for a president who came to office promising “hope” and “change”, Barack Obama has attracted a lot of criticism for providing neither – for being, in fact, much the same sort of grubby realist as his predecessors.

Probably nothing illustrates better both the power and the limitations of that criticism as the current controversy over plans for an American attack on the Assad regime in Syria.

Much of the debate seems like a rerun of the leadup to the Iraq war of 2003. Again there is a plan for unilateral action without the approval of the UN Security Council; again there is talk of weapons of mass destruction; again there is outrage on the far left; again there is what looks like a divide in Washington between bellicose idealists and peace-loving realists.

On this story, Obama has slipped effortlessly into the shoes of George W Bush. Just as he has continued warrantless electronic spying and kept Guantanamo Bay open, so he has become the defender of imperial overreach in the Middle East.

There is some truth in this critique. Many of the promoters of war in Syria are the same as those who clamored for the invasion of Iraq; they have learned nothing and forgotten nothing. And it’s a commonplace that presidents often make their predecessors’ wars their own, apparently contrary to their own inclinations – most famously, Richard Nixon in Vietnam.

But the differences between Iraq and Syria, it seems to me, are greater than the similarities. I was a strong opponent of the Iraq war from the start, and the lapse of time has not changed my opinion. But I am much less sure about the right decision to take on Syria.

The big difference, from which several others flow, is that there is already a war going on in Syria as there was not in Iraq. Fighting has been going on for more than two years, with tens of thousands killed. The United States and other western countries have already withdrawn diplomatic recognition from the Assad regime and established relations with the Syrian opposition.

This affects the legal position in at least two ways. First, intervention is not (as it was in Iraq) a matter of starting a war. America would be supporting an existing belligerent, at its request: still a serious matter (anything the US military does is serious), but no longer a breach of one of the fundamental planks of international law.

Second, the carnage in Syria raises a possible justification for intervention in the shape of responsibility to protect. In circumstances where armed intervention is the only way to head off a humanitarian disaster, international law has begun to recognise a right to act even if there is no consensus.

These differences render much of the argument of the anti-war left irrelevant. But they do not make a positive case for war. That case, it seems, has been left largely to the ancient political syllogism:

  • We must do something
  • This is something
  • Therefore, we must do this

Intervention in Syria would not be a crime, as Iraq was. But it may still be a terrible mistake.

For what it’s worth, my view is that the Syrian situation has deteriorated so much that it would be justified for the international community to authorise, via the Security Council, a broad-based intervention to impose a settlement on the warring parties. It might be a messy operation, but on balance it seems it would be better than the alternatives.

The Security Council, however, is most unlikely to act in that fashion for the foreseeable future – Russia’s veto will see to that. So it’s a separate question as to whether things are serious enough to justify unilateral action on the part of the US and its allies (not Britain now, but maybe France instead, in an interesting reversal of their Iraq roles).

Except that it’s not just a question of seriousness. The absence of UN approval doesn’t just raise the threshold of proof, it also makes success more difficult. Without at least tacit Russian support, bringing the Syrian civil war to an end will be a near-impossible task.

Obama appears to have recognised that in that he is no longer talking about intervention to secure regime change, only a limited strike to punish Assad and vindicate the international ban on chemical weapons. But although a limited action is, other things being equal, easier to justify, it is also less likely to achieve the larger goal of stopping the bloodshed and ushering in a freer Syria.

(This post is a bit of a work in progress – I intend to expand upon the theme further over the next week or two.)