Of course Jeffrey Sachs, a Sanders’ supporter, blames it on Hillary Clinton. The story is more complex. Here is what Martti Ahtisaari told the Guardian, not even mentioning Hillary Clinton!

West ‘ignored Russian offer in 2012 to have Syria’s Assad step aside’ | World news | The Guardian https://www.theguardian.com/world/2015/sep/15/west-ignored-russian-offer-in-2012-to-have-syrias-assad-step-aside

“Ahtisaari held talks with envoys from the five permanent members of the UN security council in February 2012. He said that during those discussions, the Russian ambassador, Vitaly Churkin, laid out a three-point plan, which included a proposal for Assad to cede power at some point after peace talks had started between the regime and the opposition.

But he said that the US, Britain and France were so convinced that the Syrian dictator was about to fall, they ignored the proposal.”

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“On 22 February 2012 he was sent to meet the missions of the permanent five nations (the US, Russia, UK, France and China) at UN headquarters in New York by The Elders, a group of former world leaders advocating peace and human rights that has included Nelson Mandela, Jimmy Carter, and former UN secretary general Kofi Annan.”