Addressing the historic agreement reached with Iran July 14 in Vienna, President Obama said he will "veto any legislation that prevents the successful implementation" of the deal. (WhiteHouse.gov)

For President Obama, the historic deal to limit Iran’s nuclear program reflects U.S. foreign policy and the world as it should be: Negotiation, mutual respect and rationality had triumphed over tough talk and the prospect of war.

Obama spoke at the White House on Tuesday only hours after his secretary of state concluded more than 20 months of intense negotiations with one of the United States’ oldest and most hostile enemies.

A president who often speaks of the limits of American power, especially military power, described the deal in sweeping, optimistic and even historic terms.

“The United States, together with our international partners, has achieved something that decades of animosity has not: a comprehensive long-term deal with Iran that will prevent it from obtaining a nuclear weapon,” Obama said. “This deal demonstrates that American diplomacy can bring about real and meaningful change.”

Four months ago, when the initial framework of a deal was announced, Obama cast the agreement as the only alternative to war and better than any of the bad options available to him. That speech was full of “ifs”: “If Iran violates the deal. . . . If there is backsliding. . . . If Congress kills the deal.”

On Tuesday, Obama displayed no such uncertainty as he rattled off the steps Iran will take to scale back its nuclear program: “Because of this deal Iran will remove two-thirds of its installed centrifuges,” Obama said. “Because of this deal Iran will modify its core reactor . . . because of this deal inspectors will be able to access any suspicious location.”

Taken together, these moves will extend to one year the “breakout” time it would take for Iran to produce enough weapons-grade uranium to make one nuclear bomb. All steps must be completed before Iran receives relief from the tough sanctions that brought its leaders to the negotiating table, Obama said.

Inside the White House, there have long been divisions over whether the deal was solely a mechanism to stop Iran from acquiring a nuclear weapon or something larger. “It is still just a nuclear deal,” said Phil Gordon, who formerly served as special assistant to Obama for Middle East policy. Others in the White House saw the potential in the deal to change Iranian behavior and gradually open a more positive relationship with one of the United States’ most openly hostile enemies.

Obama’s remarks, coming at the conclusion of 17 straight days of negotiation, put him squarely in the latter, more optimistic camp.

Republicans blasted Obama in the first hours after the deal for not demanding more from Iran. The agreement would not require Iran to dismantle its uranium-enrichment program, which Tehran maintains is intended only to produce fuel for peaceful nuclear energy generation. “A comprehensive agreement should require Iran to verifiably abandon — not simply delay — its pursuit of a nuclear weapons capability,” Republican presidential candidate Jeb Bush charged.

Free of punishing economic sanctions, Iran will soon have billions of dollars in new revenue that it could use to sow disorder in an already chaotic region. Republican critics of the deal said some of that money will likely be used to prop up the government of Syrian leader Bashar al-Assad or bolster militant groups and proxies such as Lebanon’s Hezbollah, Hamas in the Gaza Strip and Yemen’s Houthi rebels.

“Iran will receive billions in sanctions relief, a windfall to pursue its aggressive, destabilizing agenda in the region and beyond,” said Rep. Mac Thornberry (R-Tex.), chairman of the House Armed Services Committee. “Whatever the claimed gains we get from this deal, it clearly does not outweigh the risks to the security in the region and to the United States and its interests.”

As president, Obama has repeatedly observed that there are “no military solutions” to many of the United States’ most vexing foreign policy and national security problems. The phrase has been invoked as a mantra by the White House to explain the administration’s reluctance to plunge the country more deeply into conflicts in Ukraine, Syria, Iraq and Yemen. Often it has led the White House to accept unimaginable human suffering in places such as Syria, where millions have been killed or displaced in savage fighting.

In the Iran negotiations, Obama posited another model for exercising U.S. influence in the world. “Tough talk from Washington does not solve problems,” he said. “Hard-nosed diplomacy — leadership that has united the world’s major powers — offers a more effective way to verify that Iran is not pursuing a nuclear weapon.”

To most Middle East experts, the months of painstaking negotiations demonstrated that the Iranians, although maddening and mistrustful, are capable of making concessions. “As the revolution ages, it has become more like a normal state,” said Cliff Kupchan, an Iran specialist and chairman of the Eurasia Group. “That doesn’t mean it’s a normal state. But its trajectory is in that direction.”

Obama’s remarks at the White House suggested that he saw the possibility for something more. In April, when the general framework for the nuclear deal was reached, Iranian youths took to the streets to celebrate the accord. Obama’s Rose Garden address was broadcast live on Iranian television.

Four months later, again speaking from the White House, Obama used part of his speech to talk directly to those Iranians who yearn for a deeper connection with the rest of the world. Here Obama’s “hard-nosed diplomacy” carried a message of transformative hope that characterized his earliest and most optimistic foreign policy addresses.

“I believe that we must continue to test whether or not this region, which has known so much suffering, so much bloodshed, can move in a different direction,” he said. Even as he acknowledged differences and a difficult history that “cannot be ignored,” Obama urged Iranians to believe that “it is possible to change.”

“A foreign policy based on threats to attack your neighbors or eradicate Israel, that’s a dead end,” he said. “A different path, one of tolerance and peaceful resolution of conflict, leads to more integration into the global economy, more engagement with the international community and the ability of the Iranian people to prosper and thrive.”

Obama sought to calm the United States’ Sunni Arab allies, many of whom worry that the deal is one piece of a broader U.S. pivot toward Iran. He also promised to continue “our unprecedented efforts to strengthen Israel’s security,” and followed up those remarks later in the day with a fence-mending call to Israeli Prime Minister Benjamin Netanyahu.

The president’s main audiences, though, were the American people, a skeptical Congress and a young Iranian population that has endured tough economic times and seems eager to reconnect with this world. He warned his congressional critics of the consequences if the United States walks away from the agreement.

“Put simply, no deal means a greater chance of more war in the Middle East,” Obama said.

His message to the American and Iranian people was far more aspirational.

“This deal offers an opportunity to move in a new direction,” Obama said. “We should seize it.”