Iran has strained credulity for years with assurances that its nuclear ambitions were peaceful, our editorial today notes. The recent disputed elections and the brutality of the crackdown on protesters furthered distrust in President Mahmoud Ahmadinejad and the ruling clerics. The tension ratcheted up last week with the revelation by the Obama administration, France and Britain that Iran had a secret underground uranium enrichment facility in the works. Then came Iran's several tests of missiles capable of striking Israel, parts of Europe and U.S. military bases in the Middle East. Diplomacy may not defuse the situation. But engagement must be tried in order to work. And it will be easier to build and sustain a global coalition against Iran if its leaders are given every opportunity to stave off tough economic sanctions or other action.