Achievement of a framework agreement between Iran and six world powers to end the Islamic republic's nuclear weapons programme opens the door to a new era of policy in the Middle East with potentially far-reaching implications.
The landmark deal reached in Lausanne, Switzerland among China, Russia, France, Great Britain, Germany and the US offers Iran more than $110bn a year in sanctions relief and a return to the global economy in exchange for halting its drive for a nuclear weapon.
"Today, after many months of tough, principled diplomacy, we have achieved the framework for that deal. And it is a good deal, a deal that meets our core objectives. This framework would cut off every pathway that Iran could take to develop a nuclear weapon," Obama said in a statement delivered to reporters in Washington.
Whether the nuclear deal will lead to moderation of conflict between the US and Iran, as the West hopes, or among Iran, Israel and the US' Arab allies, remains unclear, analysts say.
"The opening of Iran, should it come to pass, is a way to really make changes in the political landscape, that could - underline could - somehow, possibly bring the Middle East to restabilising," Andrew Bacevich, an American author and professor emeritus of US military and diplomatic history at Boston University, told Al Jazeera.
For President Barack Obama, the agreement is a huge diplomatic victory and marks a sharp departure from the standoff between the US and Iran that has prevailed for decades.
"The Obama administration wants an Iran that behaves more like a normal state and the [President Hassan] Rouhani government wants a better relationship with the US. However, both sides face opposition domestically," Alireza Nader, senior international policy analyst at RAND Corp, told Al Jazeera.
The US and Iran have been locked in a hostile relationship since the 1979 Islamic Revolution and hostage-taking at the US embassy in Tehran.
"Overall, for the past 35 years, the relationship between the US and Iran has been extremely hostile. This is a huge change," said Gary Sick, a professor at Columbia University in New York who served on the White House’s National Security Council in 1979.
What the change will yield remains to be seen. Will Iran now be newly cooperative with the US and its neighbours? How will Israel and Arab nations in the region respond? Can the US balance newly competing interests in a region already torn by Sunni-Shia conflicts in Syria and Iraq. What about Yemen? All three conflicts have Iranian proxies in the fight.
"Right now the Iranian nuclear programme is preventing new approaches to all of the other issues that are troubling the Middle East," said Tom Collini, policy director at the Ploughshares Fund, an advocacy group for nuclear control and disarmament.
US Congress role
Among the major uncertainties is how the deal will be received in the Republican-led US Congress. Obama faces opposition from Republicans who control majorities in both the House and Senate.
Senator Bob Corker of Tennessee, the Republican chairman of the Senate Foreign Relations Committee, issued a cautionary statement today.
"It is important that we wait to see the specific details of today's announcement," Corker said. "We must remain clear-eyed regarding Iran’s continued resistance to concessions, long history of covert nuclear
The concessions offered to Iran in Lausanne would ensure a bad deal that would endanger Israel, the Middle East and the peace of the world
weapons-related activities, support of terrorism, and its current role in destabilising the region."
Corker has broad bipartisan support for a bill that would require the president to submit the agreement to an up-or-down vote. The White House says the bill could kill the deal and Obama has threatened to veto it should it come to his desk.
"There will be a lot of heated debate but in the end, Congress is unlikely to pass legislation calling for a down vote," Larry Hanauer, senior international policy analyst at RAND, told Al Jazeera.
Republicans, who control the Senate by a 54-44 margin with two independents who tend to vote with Democrats, are unlikely to muster the two-thirds majority needed to reject the president's policy.
If a Republican president were to be elected in two years, analysts say, it would be very difficult to reverse the international agreement with Iran by restoring multi-lateral sanctions so long as Iran is in compliance.
Continuing opposition to the agreement is expected from Israel’s Prime Minister Benjamin Netanyahu who gave a speech to the US Congress on March 3 arguing the agreement would pave the way for Iran to obtain a nuclear bomb. He reiterated his opposition as recently as April 1.
"The concessions offered to Iran in Lausanne would ensure a bad deal that would endanger Israel, the Middle East and the peace of the world," Netanyahu said in a statement.
Netanyahu's position is backed by the American Israel Public Affairs Committee (AIPAC), the largest American pro-Israel lobby group. Last month, AIPAC brought thousands of members to Washington for its annual policy conference to hear Netanyahu and meet with lawmakers on Capitol Hill.
The Obama administration's diplomatic initiative has been supported by J Street, also a pro-Israel lobby, but one open to negotiations on Iran. White House Chief of Staff Dennis McDonough spoke to the group advocating for the Iran nuclear deal.
Reassuring Arab allies
Meanwhile, the US will need to demonstrate to Arab allies - particularly Saudi Arabia and the Gulf states - it is prepared to be a reliable partner and counter Iranian involvement in the region.
"A deal will further reinforce the perception that we are acquiescing to an Iran-centric conception of the region," said Aaron David Miller, distinguished scholar at the Wilson Center, a Washington think-tank.
Analysts say the US will need to balance opportunities that arise from this new opening with Iran against meeting the interests of Saudi Arabia in the region. For example, the US is backing Saudi's military operations in Yemen against Iranian-backed Houthi rebels.
"It's important for the Obama administration to show that the US is going to maintain a robust military presence in the region and the US is going to counter Iran's hegemony," Robert Einhorn, a senior fellow for foreign policy at Brookings and former State Department official, told Al Jazeera.
Meanwhile, the sanctions relief gives President Rouhani a major domestic win that may in future translate to more political reforms and better Iranian behaviour on the world stage.
"The sanctions have been very damaging for the Iranian economy," said Shaul Bakhash, a history professor at George Mason University in Fairfax, Virginia.
Iran's oil revenues have been cut in half. Its banking system cut off from international markets. It's industrial base lacks spare parts and supplies. Medicines are difficult to obtain. The rial has depreciated by more than two-thirds against the US dollar.
While reinvigorating Iran's economy will yield benefits for its expanding middle class, Bakhash, like many observers, believes the conservative Supreme Leader Ayatollah Ali Khamenei will limit the pace of any domestic political reforms.
Technical details of the agreement are to be hammered out by the June 30 deadline for completion of the P5+1 talks, followed by crucial political hurdles to be crossed in the US Congress, at the United Nations and in Tehran.