Before leaving for the United Nations, Iran’s President Hassan Rouhani said he hoped to open a new era in dialogue with Washington. He returned to Tehran on Saturday with more in hand than even the most optimistic predictions.

Now begins the harder task for Rouhani and his inner circle of Western-educated envoys and advisers, who are suddenly partners with the White House in a potentially history-shifting reset in the Middle East that could push beyond the nuclear standoff and rival in scope the Arab Spring or Israel’s peace pact with Egypt.

To build on the stunning diplomatic openings of the past days, Rouhani and his allies now must navigate political channels that make President Barack Obama’s showdowns with his domestic critics seem almost genteel by comparison. Possibly standing in the way of Rouhani’s overtures is an array of hard-liners, led by the hugely powerful Revolutionary Guard, holding sway over nearly everything from Iran’s nuclear program to a paramilitary network that reaches each neighborhood.

What’s ahead will measure Rouhani’s resolve. It also will test how much the Guard and its backers are willing to accept something other than spite and suspicion toward the U.S. — and what it could all mean for the Guard’s regional footholds that include Syria and the anti-Israel militia Hezbollah in Lebanon.

At Rouhani’s airport arrival in Tehran, backers cheered and held aloft a placard calling him a “lord of peace,” while opponents shouted insults and chanted “death to America.”

One thing is certain, however. The rapid-fire momentum of diplomacy over the past days — fed by Twitter’s no-breather pace — cannot be maintained.

The linchpin, as always, remains Supreme Leader Ayatollah Ali Khamenei, the gate keeper for every key decision.

He has so far given critical support to Rouhani’s overtures with Washington — calling for “heroic flexibility” in diplomacy — while giving the Guard a rare scolding to keep its distance from political developments. As long as Rouhani carries Khamenei’s favor, there is unprecedented credibility to his offers to settle the impasse over Iran’s nuclear ambitions and possibly forge ahead on other fronts after a more than three-decade diplomatic estrangement with the U.S.

But Khamenei also is not interested in tearing apart the country. Strong objections from the Guard and other hard-line factions would certainly get his attention. Even a slight roll back in Khamenei’s backing for Rouhani would be magnified on the world stage, raising doubts in the West about whether it’s worth investing the diplomatic capital in mending ties with Iran.

Guard commanders had warned Rouhani last week that the time was not right for a possible photo-op hand shake with Obama at the United Nations.

Now, the Guard has to absorb the ramifications of Rouhani’s surprise 15-minute telephone call with Obama on Friday, the first direct conversation between an Iranian president and the Oval Office since the 1979 Islamic Revolution. How the commanders respond will be a telling signal of whether they will try to resist Rouhani or let events play out — at least until the next round of nuclear talks between Iran and world powers, scheduled in Geneva for Oct. 15-16.

Even hard-liners are offering mixed signals. Alaeddin Boroujerdi, who heads the parliament’s foreign policy and national security committee, said the telephone talk was a sign that Washington recognized Iran’s might. But the ultraconservative rajanews.com news website described the U.S. as an unshakable foe and dismissed Rouhani’s talk with Obama as a “strange and useless step.”

The Revolutionary Guard may often appear as the stewards of Iran’s enmity toward the “Great Satan” America, but it is not without its deft touches as well.

The Guard is something of the Pentagon, CIA and Wall Street rolled into one. Its reach extends deep into Iran’s economy through investment arms and front companies. These, too, have suffered under Western sanctions, which have included black-listing Iran from international banking systems.

Guard leaders may insist that Iran can ride out any kind of economic squeeze, but the numbers say otherwise. Iran’s inflation and unemployment are rising and — perhaps more so than political crackdowns — the stumbling economy risks feeding widespread dissent.

This may be the overriding reason for Khamenei’s green light to Rouhani’s overtures. The Guard’s leadership also does not want to be seen as blocking a chance at easing the U.S.-led sanctions.

It’s uncertain whether Washington will decide to pull back some of the embargoes as part of step-by-step bargaining in nuclear talks. Iran, too, has given offered no concrete plans on what it would do in return to address Western concerns over the country’s nuclear program.

But Secretary of State John Kerry suggested the “very different tone” from Iran could open up a new course in the negotiations, last held in April after a series of dead-end rounds. Other exchanges, including letters between Obama and Rouhani, hinted that the outreach is not only confined to the nuclear standoff and could open room for deeper contacts on many overlapping issues, including perhaps Syria’s civil war.

The West fears Iran’s uranium enrichment labs could eventually produce material for a nuclear weapon. Iran says it only seeks nuclear energy and reactors for medical research, citing a religious decree by Khamenei saying nuclear arms run contrary to Islamic values. In a possible goodwill message to Iranian hard-liners, Obama also mentioned Khamenei’s edict and promised that America did not seek “regime change” in Iran.

The Revolutionary Guard, meanwhile, knows any kind of serious rapprochement with Washington could require retooling of its regional strategies. These include being a lifeline for Syria’s Bashar Assad and Shiite factions such as Hezbollah and the forces of anti-American cleric Muqtada al-Sadr in Iraq.

At home, Iran’s Guard-directed cyber corps and drone program was created for the main purpose of countering American influence. On Friday, U.S. officials said hackers believed linked to Iran infiltrated an unclassified Navy computer network.

But there are also potential opportunities. Iran’s main rival Saudi Arabia — a close U.S. ally — would be blindsided by a diplomatic realignment in the region by Washington. The same holds for Israel, whose unwavering distrust of Iran would leave it fully out of step with the region’s political direction.

(AP)