As President Bashar al-Assad’s government falters, Syria is becoming Iran’s Achilles’ heel. Iran has poured a vast array of resources into the country. There are Islamic Revolutionary Guards Corps encampments and Iranian weapons and advisers throughout Syria. And Iranian-controlled Hezbollah forces from Lebanon have joined in butchering the Syrians who have risen up against Mr. Assad. Iran is intent on assuring its hold over the country regardless of what happens to Mr. Assad — and Israel and the West must prevent this at all costs…

Russia’s interests in Syria are not synonymous with Iran’s, and Moscow can now prove this by withdrawing its unwavering support for Mr. Assad. Russia simply wishes to maintain its access to Syria’s Mediterranean ports in Tartus and Latakia and to remain a major arms supplier to Damascus. If Washington is willing to allow that, and not to sideline Russia as it did before intervening in Libya, the convergence of American and Russian interests in Iran and Syria could pave the way for Mr. Assad’s downfall.

Once this is achieved, the entire balance of forces in the region would undergo a sea change. Iranian-sponsored terrorism would be visibly contained; Hezbollah would lose its vital Syrian conduit to Iran and Lebanon could revert to long-forgotten normalcy; Hamas fighters in Gaza would have to contemplate a future without Iranian weaponry and training; and the Iranian people might once again rise up against the regime that has brought them such pain and suffering.