Toward the end of our meeting with President Obama, one of us asked whether the Iran nuclear deal might change the future of that country's poisonously anti-American politics, and Obama drifted from the technical and political details he'd otherwise focused on into something of a more reflective tone.

"I just don’t know," he said, leaning back a bit in his chair for the first time since he'd arrived. "When Nixon went to China, Mao was still in power. He had no idea how that was going to play out.

"He didn’t know that Deng Xiaoping would suddenly come in and decide that it doesn’t matter what color the cat is as long as it catches mice, and the next thing you know you’ve got this state capitalism on the march," Obama said, paraphrasing the famous aphorism by Mao's successor that capitalistic policies were acceptable if they helped China. "You couldn’t anticipate that."

It was surprising to hear Obama, normally more restrained in how he discusses the Iran nuclear deal, refer to it, however cautiously, as a moment when the arc of history might curve.

It was one of several interesting moments during an intimate 90-minute meeting Obama held with 10 journalists in the Roosevelt Room at the White House on Wednesday. What follows is a description of that conversation and what it reveals about how the president sees the nuclear deal and the larger problems of the Middle East, as well as the opposition to the deal, a subject he returned to frequently and at times with a visceral frustration that seemed to verge on disgust.

But Obama's primary message was one of certainty. That the meeting was on the record — such gatherings, a routine event at the White House, are normally off the record — spoke to this, as did his easy manner and his eagerness to discuss fine-grained details of the deal, as well as criticisms.

"Of all the foreign policy issues that I've addressed since I've been president," he said, "I've never been more certain that this is sound policy, that it's the right thing to do for the United States, that it's the right thing to do for our allies."

I. "A possibility for change"

Since world powers had reached the agreement on limiting Iran's nuclear program, three weeks earlier in Vienna, Obama has calibrated his remarks on the deal to a narrow political mission: Get it enough support to get past Congress. That has meant emphasizing only ways in which the deal will serve US (and Israeli) security interests to limit Iran's nuclear program, and downplaying everything else.

To hear him draw a connection between the nuclear deal and China's transformation, then, was striking. It suggested that Obama, though he has repeatedly insisted he does not expect the character of Iran's regime to change, does see it as a possibility, one potentially significant enough that it evokes, at least in his mind, President Nixon's historic trip to China.

At the same time, the lesson Obama seemed to draw from the comparison was not that he, too, was on the verge of making history, but rather that transformations like China's under Deng, opportunities like Nixon's trip, can have both causes and consequences that are impossible to foresee. His role, he said, was to find "openings" for such moments.

He cited his 2012 trip to Myanmar — the first ever by a sitting president, and part of his effort to reopen the dictatorship to the world — and his detente with Cuba.

"Much of the time, we are making judgments based on percentages, and no decision we make in foreign policy is completely without hair on it"

With regards to Myanmar, also known as Burma, "we still don’t know yet how that experiment plays itself out," he said. In listing Myanmar's reforms since his trip, he mistakenly referred to dissident Aung San Suu Kyi running for president — in fact, the regime has barred her from running — before realizing his error and correcting himself. It was an unintentionally revealing comment, hinting at the ways that reforms can reverse and "openings" can close.

"We don’t know whether it’s going to get over the hump and suddenly Burma is completely transformed, or whether it retrenches as the generals in that country get scared about losing their privileges and prerogatives," he went on. "But what we’ve done is we’ve created a possibility for change."

His point seemed to be that he could imagine such a possibility for an opening in Iran as well, though the results were uncertain. He said of Iran's future, echoing his point about Myanmar, "We don’t know how it’s going to play itself out."

From there, Obama drifted back to discussing what he had brought us to the White House to discuss, which was his case for the Iran nuclear deal, which meant reasserting, as he had many times before, that the deal did not assume Iran's good behavior on nuclear issues but rather that it was a means for enforcing it.

He was careful at all times not to premise the deal on Iran's good intentions, much less the country undergoing any sort of transformation. Still, in that unguarded moment, he seemed to suggest a hope that the deal could help create "a possibility for change" all the same.

II. The question Obama didn't want to answer

Several times, Obama was asked — and resisted answering — a simple question: What is his plan if the deal falls apart?

Congress, for example, could block the deal, something that looked more possible by Friday, when Democratic Sen. Chuck Schumer announced he would oppose it. Yet while Obama was eager to talk about why killing the deal would be bad, all the ways that it would allow Iran's nuclear program to proceed and set back US foreign policy, he refused to say what he would do if that happened. At one point, when one of the journalists present began asking about his plan B, Obama cut him off, joking that he wanted to save the journalist from wasting his question.

Politically, it's understandable that he'd refuse to answer: if he says he has no Plan B, he would look foolish, but if he says he has a good plan B, he would make it easier for Republicans to justify killing the deal. Yet it's an important question.

The closest he got to providing an answer was when he was challenged on whether the only alternative to the deal was really war, as he's frequently asserted. He did not describe a clear plan B, but he did rule out a number of options.

"I do not say that a military option is inevitable just to be provocative, just to win the argument. Those are the dictates of cold, hard logic," he said.

Obama himself may not know whether he would follow through on his threat to strike Iran as a last resort

If Congress killed the deal, "doubling down on unilateral sanctions" against Iran would not be enough, he said, to get another deal. And he was "quite certain" that it would not be possible to "force our P5+1 partners [the world powers that are party to the nuclear deal] or other countries, like India or South Korea or even Japan" to go along with Congress's demand to set a new, higher bar for what the nuclear deal has to accomplish.

If that happens, he said, "we’ve sort of run out of options at that point. ... At minimum, what we’ve done is we’ve put Iran in the driver’s seat." In one scenario, he said, Iran could pull out of the deal and resume its nuclear development immediately: "The scenario that everybody talks about happening 15 years from now happens six, nine, 12 months from now."

In another scenario, Iran would declare its intention to abide by the deal. Sanctions would fall away, Russia and China would exploit the opening to hijack the process, and the US would possibly, he said, be excluded from the inspections regime and enforcement systems set up by the deal. In other words, the US would get shut out of the very process of monitoring Iran's behavior that it had set up.

"In that scenario, then, Iran is going to get some of that sanction relief anyway, and our credibility in terms of now being able to exercise any influence on how the Security Council thinks about this thing has been completely eroded," he said. "I’d have to talk to the lawyers as to what standing we would even have, since Congress would have rejected this deal, for us to be a party to it, in which case we’re not in the room, potentially."

Any of these, he said, would make it easier for Iran to grow its nuclear program and harder for the US to do anything about it: "In almost every scenario, our ability to monitor what’s happening in Iran, our ability to ensure that they are not breaking out, our ability to inspect their facilities, our ability to force them to abide by the deal has gone out the window."

Obama would not spell out what he planned to do in such a scenario, but he did say he would try to piece together a new sanctions coalition, though he was not optimistic about it. "Maybe it’s possible that for a certain period of time we can hang on to the Europeans — not certain; maybe. Maybe we can twist some arms to have some of our Asian allies hang on," he said.