Syria chemical blast: Does the West have the courage to move in?

 Is it possible that Bashar al-Assad simply lost his temper? Different reasons have been suggested to explain why the Assad regime might have launched a chemical weapons attack, risking Western intervention, just as conventional wisdom had it he was starting to win the war.

None is conclusive. But they shed light on the nature of the regime that Mr Assad leads and how, if it does act, the West intends to replace it. That last question - is there any plausible replacement for Mr Assad we can live with? - is now the key question for diplomats, military strategists and anyone who fears the backlash of another violent Middle Eastern regime change.

According to one theory put forward by the French newspaper Le Figaro, which has good access to the French military, American and even Israeli special forces are now operating in southern Syria.

They managed to forge some hand-picked rebel units into a decent grouping that was repelling previous Assad advances. The supposed presence of foreign troops infuriated Mr Assad, who activated a clause in his spokesman's statement of a year ago that the Syrian army would never use chemical weapons "against its own people". A second theory, put forward by a French academic and former diplomat long acquainted with the Assad family, sees the attack as retaliation for a close-run assassination attempt on the Syrian leader on August 8. In either case, the academic's words are worth pondering: "Bashar al-Assad's obsession, inherited from his father, is the survival of the regime, at whatever cost."

This analysis, common enough, has two implications. One is that no humanitarian consideration will outweigh the use of brute force by the regime when necessary. The second is that his very intransigence is a disincentive to the West to act. Because he is prepared to see Syrian society destroyed before being forced into exile, the West has feared until now that his departure will mean chaos beyond anything they can control. For that reason, diplomats and even Chuck Hagel, the US defence secretary, have been briefing journalists that Western intervention, however justified, would do more harm than good. "The challenge is, what does an intervention look like that has a positive outcome?" one diplomat said. But that is where Mr Assad's loss of temper - loss of control - may have changed the game.

Until now, he has been testing the lines that would trigger Western intervention, but staying on the right side. Reluctant to get involved in the Middle East at all, let alone militarily, both Barack Obama and David Cameron talk of wanting Mr Assad's removal but the arguments against, strongly put by members of their own parties, have always outweighed the risks. However the longer they hesitated, the worse those risks got, with the opposition more disunited and Syria looking more and more like its neighbour Iraq.

The war is now a running sore imperilling Iraq, Lebanon, Jordan, Turkey and more. Mr Obama, whether he likes it or not, will be held responsible if the Middle East implodes on his watch. His only alternative to that outcome now is to try actively to reshape it. That is why the chemical weapons attack, if proved, is so important: it allows more than a punitive response. It allows the United States and its allies, should they choose, to go in with such force that they can decide who replaces him and how the Middle East responds. Already, reports talk of hundreds of tons of arms pouring into northern Syria, to be distributed among "favourable" - in other words, non-jihadist - rebel groups. The US navy is moving in and Britain is readying its forces. Does Mr Obama have the courage, some would say foolhardiness? This would not just be intervention. It would be a decisive attempt to mould the future of the region, before it fell apart.