He attempted to preempt critics by stating that the deal “meets the national security interests of the U.S. and its allies,” and he reminded his listeners that the sole priority has always been to stop Iran from developing a nuclear weapon.

Obama also made clear that the accord is not a prelude to a normalization of relations with Iran or to formal cooperation with Tehran in the fight against the Islamic State, but Washington does hope to be able to “incentivize (the Iranians) to behave differently in the region.”

The president made his remarks at a press conference focusing on Iran, one day after negotiators in Vienna reached the agreement between the Iranian government and the P5+1 group consisting of the United States, Russia, China, France and the United Kingdom, plus Germany.

Obama told reporters at the White House that the chance for reaching agreement with Iran might not occur again in “our lifetimes,” and he said that if the United States does not seize the opportunity “future generations will judge us harshly.”

The president spoke directly with reporters, but his real audience appeared to be Democrats on Capitol Hill who have been skeptical of the deal, and consequently who might join Republicans in trying to sink the pact.

The administration launched its campaign defending the accord to lobby the public and lawmakers to support the pact, and now Congress has 60 days to review it and then will have the option to vote – probably in September – to approve or reject it.

Obama has vowed to veto any bill that threatens the accord and it would require a two-third majority in both houses of Congress to override the veto, meaning that dozens of the president’s fellow Democrats would have to join Republicans in opposing the agreement.

Obama said that he expects the debate on the pact to be robust and said that so far “nobody” has presented an alternative to a pact that is supported by “99 percent of the world community.”

“There really are only two alternatives here: either the issue of Iran obtaining a nuclear weapon is resolved diplomatically, through a negotiation, or it’s resolved through force, through war. Those are the options,” Obama said.

“Without a deal,” he said, “there would be no limits to Iran’s nuclear program and Iran could move closer to a nuclear bomb ... Without a deal, we risk even more war in the Middle East.”

Furthermore, he said that “It is incumbent on the critics of this deal to explain how an American president is in a worse position – 12, 13, 14, 15 years from now – if, in fact, at that point, Iran says, ‘We’re going to back out of the (deal), kick out inspectors, and go for a nuclear bomb.’”

“With this deal we cut off every one of Iran’s pathways to a nuclear weapons program,” he said. “Without a deal, those pathways remain open, and Iran could move closer to a nuclear bomb.”

“I can say with confidence, but more importantly, nuclear experts can say with confidence: Iran will not be in a position to develop a nuclear bomb” under the agreement, Obama said.