One of the key questions surrounding the Iranian nuclear deal is what it means for the country's so-called "breakout time." That's the length of time Iran would need to produce enough highly enriched uranium to make one nuclear weapon.
The deal would limit Iran's nuclear activity in ways that stretches the breakout time. There's a general consensus that the current breakout time is around two to three months, and that would be extended to around a year under the agreement.
If Iran violated the deal and decided to go for a bomb, the international community would then have time to respond.
President Obama first discussed this with NPR in April. He acknowledged that as the agreement ages, and some provisions expire, the breakout time goes back down.
"What is a more relevant fear would be that in year 13, 14, 15, they have advanced centrifuges that can enrich uranium fairly rapidly, and at that time the breakout times would have shrunk almost down to zero," Obama said in April.
But the president says that's well in the future and the deal would buy time.
"Essentially we're purchasing, for 13, 14, 15 years, assurances that the breakout is at least a year," the president said.
Critics didn't see it that way. Obama's forecast of an eventual breakout time near zero made headlines back in April. It was repeated by opponents and the media for months.
The State Department said the president misspoke. But opponents say he told the truth. And those critics include Israeli Prime Minister Benjamin Netanyahu.
Last month, Netanyahu told NPR's David Greene the deal eventually frees Iran.
"They'll be very close to breakout. I think President Obama, in one of his previous interviews, said at that point they could have effectively zero breakout time to the bomb, and that, unfortunately, is true," Netanyahu said. "If the idea is 'at least we get them away from the bomb,' no you don't."
Netanyahu says the deal only delays Iran's nuclear threat. And U.S. lawmakers skeptical of the nuclear deal have said delaying the threat is not enough for them.
So NPR's Steve Inskeep asked the president about this again:
INSKEEP: Prime Minister Netanyahu of Israel has argued that as the agreement begins to expire, 13, 14, 15 years from now, the breakout time goes back down to near zero.
INSKEEP: And in saying that, he quotes you in an interview with us, in which you made a statement that was later clarified.
INSKEEP: I just want to be absolutely clear on this. Fifteen years from now, as some provisions expire, what is Iran's breakout time going to be?
OBAMA: Well, it shrinks back down to roughly where it is now.
INSKEEP: Which is close to zero?
OBAMA: Well, which is a matter of months.
But the president says the deal is still a good one. Here's his explanation:
"If in fact the breakout times now are a few months, and we're able to push that breakout time out to a year so that we have more time and space to see whether or not Iran is cheating on an agreement, kicking out inspectors, going for a nuclear weapon, if the breakout time is extended for 15 years and then it goes back to where it is right now, why is that a bad deal?"
In the president's view, the world gets extra security for 15 years, and by then Iran's government, or its interests, may change.
Even if not, weapons inspectors will remain at work permanently.
The president says his critics are ignoring the idea that it's good to buy time.
"And what that tells me is that there may be ideological opposition to doing any business with Iran," he adds.
It would be more honest, he contends, if his critics admitted they don't favor any diplomacy with Iran.
"If you just say, 'We don't think you should deal with Iran,' then that at least has a logic to it," the president said. "If you're saying, though, that this is an issue that can't be resolved diplomatically and you share my view that Iran can't get a nuclear weapon, then you really are narrowing your choices at that point."
Congress plans to vote next month on whether to reject the nuclear deal. If Congress opposes the agreement, the president can veto the move. Both houses would then need two-thirds majorities to override a presidential veto and block the deal.
The president is framing the congressional vote as a narrow choice indeed: Accept the negotiated agreement, with all its complexities and risks, or take a risk on chaos and even war.