As the Syrian crisis has reached the tipping point and the fall of Bashar al-Assad's regime seems to be a matter of time, Israel has abandoned the passive stance it has maintained since this crisis began in March 2011. Israel's leaders and security establishment are now looking at the potential ramifications of the regime's collapse as imminent policy challenges. Uppermost in their minds is the danger that Syria's stockpiles of missiles and chemical and biological weapons fall into the hands of jihadis who have penetrated Syria and the Syrian opposition, or be handed over to Hezbollah in Lebanon.

Israel's position with regard to the Syrian crisis has been misrepresented by two myths. One, propagated by the Assad regime itself, has argued from the outset that this is not a genuine domestic rebellion, but a conspiracy hatched by the US and Israel. The other holds that Israel favours the survival of Assad's regime ("the devil we know" theory) and has exerted its influence in Washington in order to dissuade the Obama administration from serious humanitarian intervention in Syria.

This myth is predicated on pre-2006 reality. In 2005, when President Bush wanted to go after Assad, Israel's prime minister at the time, Ariel Sharon, did indeed caution him against the consequences of such action. But Israel's 2006 war in Lebanon and the discovery of the North Korean nuclear reactor in Syria in 2007 changed Israel's perception of Assad from "the least of all evils" to just "evil". In any event, once the rebellion broke out Israel realised that its best option was to keep a passive stance. Even if it wanted to support the rebels or offer humanitarian help, it knew it would be playing into the hands of the regime, which was certain to use any support to substantiate its claim that the rebels were doing Israel's bidding. Israeli analysts and policy planners were busy studying the repercussions of the regime falling and its replacement by competing opposition groups, but these were hypothetical exercises.

During the past few weeks, as the regime's collapse became more plausible and imminent, Israel has shifted from hypothetical scenarios to dealing with concrete threats. Israel is, of course, concerned with the future of the Syrian state. It is an important neighbour, and chaos or the emergence of a radical Islamist regime would be very negative developments for a country whose geopolitical environment has already been clouded by the Arab spring. Spillover effects into Lebanon or Jordan are also a matter of concern for Israel. These potentially adverse repercussions would be offset to some extent by the blow to Iran's position and influence and the weakening of Hezbollah.

In looking at these issues Israel bears in mind that its ability to affect the course of events in Syria remains very limited. This is not the case, however, with regard to two threats. One is the possibility that the a crumbling Syrian regime may fire its missiles into Israel in order to depart in a Samson-like blaze of glory. Not very likely, but something the IDF's command needs to take into account. More likely is the danger that Syria's stockpiles of WMD fall into or be delivered into the wrong hands. This is an eventuality that Israel can respond to by interception. Israel's (and Washington's) concern is that such action could easily develop into a regional war involving Hezbollah, and possibly Iran.

The way to pre-empt it is for Israel and the US to continue their discreet dialogue and for Washington to try to persuade Moscow to abandon its sweeping support for Assad's regime and to co-operate at least in this issue, if not in guaranteeing a smoother transition to a new political order in Syria. So far Vladimir Putin has been obsessed by his anxiety that this traditional Soviet and Russian fief would fall into pro-western hands. It is time he realised Assad's ship is sinking and Moscow would be best served by looking at the new phase and by helping to prevent a major crisis from erupting.

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