President Barack Obama defended the framework agreement on Iran’s nuclear program Sunday, calling it a “once-in-a-lifetime opportunity” and adding that the deal has a chance of success because of how much bigger and more powerful the U.S. is compared to Iran. “Iran understands that they cannot fight us… You asked about an Obama doctrine. The doctrine is: We will engage, but we preserve all our capabilities,” he told The New York Times’ Thomas Friedman. Obama argued his diplomatic approach to preventing Iran from getting nuclear weapons was part of his administration’s broader strategy in regard to warming relations with Cuba and Myanmar. “We are powerful enough to be able to test these propositions without putting ourselves at risk. And that’s the thing... people don’t seem to understand,” he said.