At the bottom of President Obama's confidence is his knowledge that only in Israel and the U.S. is this agreement at all controversial. Let's keep this really simple: if Iran chooses to build a nuclear bomb it will. Just like Israel did. And just like North Korea did, and Pakistan, and India.
If they have backed off that - and they have - for 10, 1, 25 or more years (depending on how you read the Agreement) it is because they made a rational calculation that shutting down centrifuges was worth the price. If you want abject surrender (viz. the insufferable David Brooks) you should remember that Iran lost 1 million in it war with Iraq. (A war in which we tilted to Saddam Hussein).
President Obama Defends the Iran Deal After His American University Speech - The Atlantic
by James Fallows