Not since Richard Nixon shook hands with China's Communist revolutionary leader Mao Zedong in Beijing more than 40 years ago has a U.S. president so upended long-standing American policy to reach out to a bitter adversary.
Barack Obama's extended hand to Tehran's ruling mullahs may turn out to be as much of a game-changer as Mr. Nixon's bold opening to Beijing in 1972.
Mr. Obama isn't likely to be headed for Qum to take tea and talk ping-pong with Supreme Leader Ali Khamenei, but years of back-channel talks with Tehran and exchanges of letters set the stage for this week's breakthrough just as surely as Henry Kissinger's secret China diplomacy did four decades ago.
And while Mr. Nixon's legacy will be forever tainted by his domestic skullduggery that ended in historic disgrace and resignation, Mr. Obama's nuclear pact with Iran may prove the shining foreign-policy achievement that salvaged an otherwise grim record on the international stage.
It may takes decades to determine if Mr. Obama's willingness to ditch the certainties of an adversarial standoff with a hostile state that – if necessary – could be bombed into defeat actually produces a more peaceful Middle East.
Still, that's what's at stake. The nuclear-limitations deal is just the beginning of a new era in U.S.-Iranian relations, just as Mr. Nixon's parlay with China's Communist regime recast the Cold War and changed the triangulation of Sino-Soviet-American relations.
"The deal validates President Obama's campaign theme of engaging with adversaries," Suzanne Maloney, a senior fellow at the Brookings Center for Middle East Policy, wrote this week. "In a broader sense, it should serve as a reminder to a cynical American citizenry (and an even more cynical policy community) that negotiations can yield real results, and that the investment of time and talent can – at the very least – begin to offer solutions to international problems that had long seemed intractable."
Critics accuse Mr. Obama of capitulation and appeasement, of being so needy for a foreign policy success that he sold out U.S. interests and Israel's security just to get it done.
Mr. Obama has tried to temper expectations of dramatic swift change, pointing to a long list of deep and unresolved differences. "We'll still have problems with Iran's sponsorship of terrorism; its funding of proxies like Hezbollah that threaten Israel and threaten the region; the destabilizing activities that they're engaging in, including in places like Yemen," he said this week.
But he clearly hopes for more. And he demonstrated a willingness to treat Tehran as a powerful regional player rather than shunning it as a terrorist-sponsoring pariah state fit only to be threatened and contained. That changes every equation in the Middle East.
The Obama administration and Tehran's Islamic regime already have some shared strategic objectives, and while both deny any "co-operation," the military reality on the ground suggests otherwise. U.S. warplanes in the air and Iranian Quds Special Forces on the ground are attacking the same Islamic State targets in Iraq. Both Tehran and Washington are propping up the fragile government in Baghdad.
Even where they differ, Mr. Obama now accepts that Tehran is a major regional player with a vital role and that without Iran, some solutions are impossible.
"I do agree that we're not going to solve the problems in Syria unless there's buy-in from the Russians, the Iranians, the Turks, our Gulf partners," the President said this week, specifically adding Iran, to the usual list. To achieve an end to the Syrian war, "there's going to have to be agreement among the major powers that are interested in Syria that this is not going to be won on the battlefield. Iran is one of those players, and I think that it's important for them to be part of that conversation."
The United States working with Iran as part of the solution – that's the stuff presidential legacies are built on, even if Mr. Obama dare not trumpet too loudly or too soon.
Playing the Iran card may also be Mr. Obama's best hope of salvaging some achievement in the region, which has otherwise spiralled into widening war, chaos and suffering on his watch.
The key foreign-policy promise that got him elected – pulling all U.S. troops out of Iraq – has gone sour, with that nation racked again by war and on the verge of collapse. The U.S.-led air war in Libya toppled a dictator but the country remains torn by violence. Syria has collapsed into bloody civil war, the violent jihadis of Islamic State control far more territory and inspire a far greater following for their dream of an extremist caliphate than al-Qaeda ever managed. And U.S. professions of support of democracy in the heady wake of the Arab Spring have retreated back into support of authoritarian regimes as long as they keep order. And U.S.-Israeli relations are at a historic nadir.
Dealing with Iran won't change all that, but it does match Mr. Obama's long-asserted preference for parlaying with adversaries.
Just as he has with Cuba, the President threw out decades-old dogma about shunning hostile regimes. But unlike with Iran, normalizing relations with the enfeebled Cuban regime posed no geopolitical risks and offers no great strategic advantage. Even if closer ties with Havana proves to be a terrible mistake, the costs are inconsequential compared to getting it wrong with Tehran.
"Whether you like it or not, this agreement is a big deal," Aaron David Miller, an adviser on the Middle East to both Democratic and Republican administrations and now a Distinguished Scholar at the Woodrow Wilson Center, a Washington think tank, wrote after the deal was done. "For almost 40 years, Washington based its Iran policy on containment and confrontation. But from now on, the default position will be co-operation. This doesn't mean the beginning of some Golden Age in U.S.-Iran relations.
"But the efforts to keep this accord alive will create new patterns of behaviour, new efforts to thaw other iceberg issues, and an inclination to test whether Tehran is ready to co-operate on regional matters," he added. "The Obama administration will have little choice but to play this game. After all, this is President Obama's signature Middle East success, and he will go to great lengths to protect it. The President was never interested in regime change. What he wants is to change regime behaviour."
That rather echoes Mr. Nixon's assessment. "This was the week that changed the world," he said after his rapprochement visit to Beijing, adding that the real importance lies in what will be done "in the years ahead to build a bridge across 16,000 miles and 22 years of hostilities which have divided us in the past.'