Calls to ease sanctions on Iran to spur global negotiations over its nuclear program will backfire, making a deal far less likely and greatly raising the risk of an Israeli military strike to cripple the program.To its proponents, sanctions-easing is a necessary confidence-boosting measure to assure Iran that the United States and the other “P5+1” negotiators — Britain, France, Germany, Russia and China — want a deal.But, it was the ever-tighter global, U.S. and European sanctions of recent months on Iran’s energy and financial sectors — not global concessions — that forced Tehran to the table. And it’s the still-tighter sanctions on the horizon — especially the July 1 start of Europe’s embargo on Iranian oil — that will keep it there.That’s because Iran’s economy is suffering, stoking greater domestic anger at a regime that’s already widely despised across the Islamic Republic. Tehran will only strike a deal if it faces the prospect that greater economic disarray will generate the requisite anger that would threaten the regime’s grip on power.Currently, Iran is having trouble selling its oil and its banks are increasingly shut out of the global financial system.