Wearing pinstripes and a pince-nez, Staffan de Mistura, the United Nations envoy for Syria , arrived at the Security Council one Tuesday afternoon in February and announced that President Bashar al-Assad had agreed to halt airstrikes over Aleppo. Would the rebels, Mr. de Mistura suggested, agree to halt their shelling? What he did not announce, but everyone knew by then, was that the Assad government had begun a military offensive to encircle opposition-held enclaves in Aleppo and that fierce fighting was underway. It would take only a few days for rebel leaders, having pushed back Syrian government forces, to outright reject Mr. de Mistura’s proposed freeze in […]