Here's a proposal by Mehdi Khalaji, a specialist on Shi'a and Sunni politics in Iran and Iraq, now a senior fellow at the Washington Institute for Near East Policy. Khalaji knows the impediments and the risks.  If such an approach does not work we will all know where we stand.  The U.S. will know, the rest of Europe will know.  Even the Russian Federation might take cognizance of the grim facts.  And if the facts are not grim so much the better...