Yesterday, in an announcement that took pretty much all news networks and commentators by surprise, Barack Obama took precisely zero military action in response to Syria's highly-publicised recent use of chemical weapons.

For even the first few paragraphs of his speech, everyone still assumed there would be Tomahawk missiles in the air within hours.

“In a world with many dangers, this menace must be confronted. Now, after careful deliberation, I have decided that the United States should take military action against Syrian regime targets,” the President said. “I’m confident we can hold the Assad regime accountable for their use of chemical weapons, deter this kind of behaviour, and degrade their capacity to carry it out. Our military has positioned assets in the region. The Chairman of the Joint Chiefs has informed me that we are prepared to strike whenever we choose.”

So far, so Desert Fox. But then, the President changed tack.

“I’m also mindful that I’m the President of the world’s oldest constitutional democracy,” he said, in one of the more awkward non-sequiturs of his speaking career. “I’ve long believed that our power is rooted not just in our military might, but in our example as a government of the people, by the people, and for the people. And that’s why I’ve made a second decision: I will seek authorisation for the use of force from the American people’s representatives in Congress.”

That's right: despite not technically needing the approval of his legislature to take military action, Obama is magnanimously seeking it anyway. This would be a big deal even if there wasn't an enormous elephant in that particular room, but of course there is, in the form of David Cameron's catastrophically embarrassing failure to achieve the exact same vote, despite – in theory – having a much tighter constitutional hold on his legislature than Obama.

But the US president has run out of friends. The UN is completely gridlocked by Russia, while the UK, America's usual ally in such adventures, now isn't on board either. Nobody, not the Arab League, not NATO, not the war-weary American public nor even the war-eager hawks in the Republican party for whom limited missile strikes don't go far enough; nobody, except suddenly belligerent France, is on board with the President's plan.

That being the case, Obama has decided to duck acting unilaterally. Instead, he is betting on his own ability to sell the war to the people, and therefore to Congress, in just nine days. If he succeeds, of course, he can go to war without being accused of riding roughshod over Congress, and international law. He cannot be accused of acting alone.

But if he fails, it will be a catastrophe for his credibility at home and abroad.

This is Obama's own fault, really. He talked himself into a corner with his 'red line' ultimatum, and has found himself cornered between two versions of himself: one, a year ago, laying down the sanctity of international law on chemical weaponry; and the other as a candidate in 2008 waxing lyrical on how the primacy of Congress should be respected in warlike matters. The latter position makes going to war alone, without Congress, the UN, a national mandate, or even the British along for the ride, unpalatable. So, with his position on chemical weapons staked out in 2012, but no support, and mindful of what he said about similar decisions as a candidate in 2008, he has taken the less lonely option. He has chosen to look like a coward, instead of a hypocrite.

Is that entirely fair? Was this cowardice? To some extent, yes. To the Syrian rebels who had been expecting air support, it looks like when the crucial moment came, America blinked. After more than two years of inaction, their disappointment is unsurprising.

One thing is certain: Obama is not really acting out of concern for constitutionality. Remember, he had no such misgivings about not consulting Congress when he took action in Libya two years ago. But then, he had UN backing for that; this time he faced standing alone. So he passed the buck.

Which is not to say that, paradoxically, shoving the responsibility for this decision on to Congress wasn't in its own way a brave move. After Cameron's humiliation in the Commons last week, Obama will be acutely aware that a losing vote now, after he so clearly staked out his own position, would be worse than embarrassing: it could be seen as a de facto vote of no confidence in his administration. The stakes could not be higher.

With Congress away for the Labor Day holiday, he has until 9 September to make his case. Obama would not have taken this risk unless he had reasonable confidence that he is going to succeed – but the American legislature is notoriously unpredictable, obstructive, and – in the case of the House of Representatives – controlled by the Republican party. There are factions who are going to make his job difficult: libertarian Republicans and dove Democrats want to leave Syria alone to fight its own civil war; and on the other side, interventionist Republicans like John McCain think targeted strikes don't go far enough.

Coward or not, the President now has a hell of a fight on his hands - before an American shot has been fired.