President Obama was in a reflective mood when he met with a group of journalists at the White House on Wednesday afternoon, a few hours after he delivered a combative speech defending the Iran deal. He is, in private meetings, a congenial stoic, even as he chews Nicorette gum to stay ahead of an old vice. But his frustration—that the bigger message of his foreign policy is being lost in the political furies over Iran—was conspicuous. He made clear that the proposed deal—the most ambitious foreign-policy initiative of his Presidency—is less about Iran than about getting America off its war track; Obama believes that Washington, almost by default, too often unwisely deploys the military as the quickest solution to international crises.

Obama makes many of his pitches in the Roosevelt Room, a modest, windowless chamber with a conference table. When the West Wing was built, in 1902, it was originally the President’s office. A portrait of Franklin Roosevelt is on one wall; a picture of Teddy Roosevelt, as a Rough Rider on horseback, hangs over the fireplace. The most striking piece in the room is the smallest: The 1906 Nobel Prize, the first won by an American and the first by a U.S. President, is encased behind glass. It went to Teddy Roosevelt for mediating an end to the Russo-Japanese war. Only two other Presidents--Woodrow Wilson, for the League of Nations, and Jimmy Carter, after leaving office, for promoting human rights—had won it before Obama was named, just months after his election, more for his spirit than any specific achievement. As he enters the final eighteen months of his Presidency, he seems to want to prove that he deserves it.

Obama chose to give the Iran speech on the American University campus, where John F. Kennedy told the 1963 graduating class, "The United States, as the world knows, will never start a war. We do not want a war. We do not now expect a war. This generation of Americans has already had enough—more than enough—of war and hate and oppression."

Perhaps it’s the professor in him, but Obama can’t seem to understand why some Americans now interpret diplomacy as weakness, especially given the nation’s recent experience in conflict. In the Roosevelt Room, he said, “We underestimate our power when we restrict it to just our military power. We shortchange our influence and our ability to shape events when that’s the only tool we think we have in the toolbox.”

After six and a half years in office, Obama said that the tough calls—to redeploy American troops to Iraq or to mobilize NATO to launch airstrikes against Libya—have convinced him more than ever of the need to make force a last resort. “In terms of decisions I make, I do think that I have a better sense of how military action can result in unintended consequences,” he said. “And I am confirmed in my belief that much of the time we are making judgments based on percentages, and no decision we make in foreign policy—or, for that matter, any policy—is completely without hair, which is how we kind of describe it. ... There’s always going to be some complications.”

The President leaned back in a leather chair pulled up to the center of the table. “So maybe at the same time as I’m more confident today, I’m also more humble,” he said. “And that’s part of the reason why, when I see a situation like this one, where we can achieve an objective with a unified world behind us—and we preserve our hedge against it not working out—I think it would be foolish, even tragic, for us to pass up on that opportunity.”

He noted that his predecessors, both Democrats and Republicans, had successfully used diplomacy to prevent nuclear proliferation. “Both President Kennedy and President Reagan were roundly criticized by parts of the foreign-policy establishment that felt they were being weak by engaging our adversaries,” he told us. “So some of it is built into a political lexicon that makes you sound tougher if you don't talk to somebody, and, rather, very loudly, wield a big stick. I also think that there is a particular mind-set that was on display in the run-up to the Iraq War that continues to this day. Some of the folks who were involved in that decision either don’t remember what they said or are entirely unapologetic about the results.”

Compared to historic pacts, such as the SALT and START treaties brokered with the Soviet Union, Obama views the Iran deal as one of the best arms agreements in half a century. “In past agreements of this sort—of this magnitude, at least—we typically had to give something up,” he said. “We were having to constrain ourselves in significant ways. In that sense, there was greater risk. In this situation, we do not surrender our capabilities to break the glass and respond if, in fact, Iran proves unable or unwilling to meet its commitments.”

Obama was unapologetic about dealing with the Islamic Republic, which is held responsible—directly or indirectly—for the deaths of thousands of Americans. Three Iranian-Americans are still detained in Iran; a former F.B.I. agent disappeared on an Iranian island in 2007. The Administration is not counting on the possibility that a deal over Iran’s nuclear program will alter Iran’s politics—or produce détente.

“There is nothing in this deal that is dependent on a transformation of the character of the Iranian regime,” Obama said. “This does not represent a strategic rapprochement between the United States and Iran. This is a hardheaded, clear-eyed, calculated decision to take—to seize our best opportunity to lock down the possibility of Iran getting a nuclear weapon.”

Obama said that he took Supreme Leader Ayatollah Ali Khamenei, who has been in power a quarter century, at his word, especially on Israel. “His ideology is steeped with anti-Semitism, and if he could, without catastrophic costs, inflict great harm on Israel, I’m confident that he would,” the President said. Even so, he went on, “It is possible for leaders or regimes to be cruel, bigoted, twisted in their world views and still make rational calculations with respect to their limits and their self-preservation. And what we’ve seen, at least since 1979, is Iran making constant, calculated decisions that allow it to preserve the regime, to expand their influence where they can, to be opportunistic, to create what they view as hedges against potential Israeli attack, in the form of Hezbollah and other proxies in the region.”

The President also warned Congress that, if it rejected the deal, the biggest winners in Tehran would be the most hard-line factions.

I asked the President how the ongoing chants of “Death to America” by Iranian crowds influenced his thinking during the twenty months of difficult negotiations. “It’s not appealing to deal with countries that express hatred towards us. It wasn’t easy to negotiate arms agreements with a near military peer”—the Soviet Union—“that could blow up every American city,” he said. “But, when it comes to arms-control agreements, or nonproliferation agreements of any magnitude, by definition you’re generally dealing with those folks. I don’t have to negotiate an arms agreement with Great Britain or with France.”