After a roller coaster week of round-the-clock diplomacy, the United States and its five international partners managed to hammer out the key provisions of an accord that Washington has been pursuing for nearly a decade — a deal to verifiably constrain Iran’s expansive nuclear program. President Barack Obama hailed the announcement as a “historic understanding with Iran which, if fully implemented, will prevent it from obtaining a nuclear weapon. I am convinced that if this framework leads to a comprehensive deal, it will make our country, our allies, and our world safer… It is our best option by far.”

It is not a final deal — not by a long shot — but the framework announced on Thursday was far more substantive than many had been expecting. And it appeared to make good on what the president previously indicated he would require to sustain the talks until the final deadline of June 30: serious evidence that the parties can reach a deal that meets the international community’s requirements for ensuring Iran does not achieve nuclear weapons capability.

The announcement followed some apparent turbulence in the negotiating process. Expectations rose in February and early March, as reports suggested that the most troublesome technical differences surrounding Iran’s enrichment capabilities had finally been overcome. However, these hopes were dashed as the talks began earlier this week, when Iranian negotiators appeared to scuttle hard-won progress on the issue of Iran’s handling of its stockpiles of enriched uranium.

For days, the world’s attention remained trained on the talks in Lausanne, Switzerland, where representatives from Tehran, Washington, the European Union, and five other world powers met in sessions that dragged late into the night — and sometimes well into the following morning. Their endurance was a reflection of the political stakes. As I wrote earlier this week, the March 31 “target date for achieving a political framework was meant to be a soft deadline — a deliberately low hurdle that both sides would use to reassure their impatient domestic critics that a comprehensive deal was, in fact, achievable. But those same partisan pressures — amplified by escalating regional unrest — conspired to transform this purported ‘soft deadline’ into a moment of truth for the tortuous process and, by extension, for the Obama administration’s Middle East policy.”

That moment of truth became a moment of rare triumph for Obama’s foreign policy. What the negotiators managed to produce appeared to validate Obama’s decision to remain at the table for almost 48 hours past the March 31st deadline. Instead of a general statement of progress that Iranian officials had been foreshadowing, the framework announced on Thursday outlined in some considerable detail the shape of a long-term agreement on Iran’s nuclear program and the nature of the reciprocal trade-offs.

What turned the tide? Maybe it was the baby gifts emblazoned with the MIT logo gifted by U.S. Energy Secretary Ernest Moniz to his fellow alumnus, Ali Akbar Salehi, the head of Iran’s Atomic Energy Organization, to mark a grandchild’s birth. Maybe it was the oddly reverential condolences offered by Secretary of State John Kerry to Hossein Fereydoun, advisor (and brother) to Iranian president Hassan Rouhani after the death of Rouhani’s mother. Maybe it was the epic all-nighters or the ambience of a series of Swiss hotels.

Whatever the case, the administration’s gamble — and the tenacity of Kerry and his colleagues and counterparts — has paid off for now. But there are at least four big issues that confront the Obama administration as it seeks to achieve a true resolution to this longstanding crisis.

Divergent American and Iranian interpretations of the deal

One of the biggest red flags about today’s announcement is that while Iranian Foreign Minister Mohammad Javad Zarif and European Union foreign policy chief Federica Mogherini issued a brief and relatively vague joint statement, there was no official text released that outlines any actual agreement among the seven parties. News of the terms of the deal began to trickle out in the Iranian media in the moments before Mogherini and Zarif spoke, and the White House followed up shortly thereafter with a two-page fact sheet.

Here’s the rub, though — despite the apparent breakthrough, the official American and Iranian narratives of what was agreed upon differs considerably, and in crucial dimensions. While the White House version asserts that “Iran has agreed to reduce its current stockpile of about 10,000 kg of low-enriched uranium (LEU) to 300 kg of 3.67 percent LEU for 15 years,” the Iranian synopsis of the framework omits any reference to such a reduction.

Meanwhile, in Tehran’s telling, the agreement would provide far-reaching and effectively permanent repeal of European and American sanctions, while Washington instead suggests that Tehran will see only the nuclear-related sanctions suspended — not revoked — only after “after the IAEA has verified that Iran has taken all of its key nuclear-related steps.” The U.S. version also emphasizes snap-back provisions that would lead to the automatic re-imposition of US and European measures if Tehran failed to comply with the terms of the deal, while the Iranian text does not reference this at all.

These are only a few of the considerable discrepancies between the two official accounts of the parameters that were supposedly agreed upon in Lausanne. These differences are potentially deeply problematic, as they suggest that a deep divergence on key issues remains. And they undercut the Obama administration’s credibility in selling the deal to its domestic critics, who harbor profound distrust of Tehran and will use the discrepancies to suggest that Tehran is already backing away from any commitments made even before the deal has been finalized.

Zarif interrupted his victory lap on social media (applications which his government conveniently bans ordinary Iranians from using) to snipe at Washington for its summation of the deal. Opportunistic public posturing is to some extent inevitable, but Washington and its partners will watch closely how the deal is sold to key constituencies within the Iranian political elite, most importantly the players closest to Iran’s supreme leader, Ayatollah Ali Khamenei. Looming large in any such scrutiny is the experience of October 2009, when Iranian negotiators appeared to sign off on a preliminary understanding for a confidence-building gesture in discussions with the P5+1 representatives, only to back away from the arrangement after returning to Tehran and experiencing opposition from Khamenei and other heavyweights (including, it should be noted, Hassan Rouhani).

The devil is in the details

To some extent, the dueling narratives are a reflection of the fact that today’s agreement remains very much a preliminary one. It is an understanding of general parameters, not a meticulously-parsed final legal text. As President Obama conceded in his statement, “nothing is agreed to until everything is agreed to.” Even if one was to disregard the apparent divergence between the Iranian and American spin on those parameters, negotiators would still be facing a formidable task to clarify all the outstanding issues that are not addressed by today’s framework agreement.

As noted above, there is some discrepancy surrounding reductions in Iranian stockpiles of enriched uranium. If in fact the U.S. fact sheet is correct, and Tehran is committed to extensive reductions in its stockpile, how will this in fact be implemented? On sanctions, Obama suggested in his statement that sanctions relief would be “phased in.” However, there is nothing in the statement issued in Lausanne, or the U.S. fact sheet, that references such sequencing or details its timeline. There are literally dozens of similar questions that can be raised about every element of today’s apparent bargain, and a final, comprehensive agreement will need to be fleshed out in excruciating detail in order to ensure its successful execution. This week’s grueling negotiations, which saw talks run almost around the clock as previously agreed-upon provisions suddenly came up for dispute, offers only a small preview of the painstaking, exhausting task that must be achieved in the next 90 days.

What will Congress do?

All these negotiations will have to play out in an environment of fierce domestic contention over the terms of a deal, most especially in Washington. Several of the leading Republican contenders for the White House in the 2016 race have already come out against the framework announced today, and Congress has proven a major thorn in the side of the administration on its Iran policy throughout much of Obama’s two terms. The White House is going to have to contend with at least one measure aimed at limiting the president’s authority to sign and implement a deal without congressional support.

While supporters of additional sanctions on Iran have indicated that they will hold off during the race to conclude the final deal by June 30, other legislative proposals are likely to move much more quickly.

A bill sponsored by Senator Bob Corker (R-TN) that would give the Congress an up-or-down vote on any final deal has already garnered support from at least 64 senators. As my colleague William Galston, who is Brookings Ezra K. Zilkha Chair in Governance Studies, has noted both in his writing and in our discussion on the deal earlier this week, nearly two-thirds of Americans believe that Congress should have the right to approve any nuclear deal with Iran.

It remains to be seen how the agreement today influences the debate on the Hill. Congress returns from the Easter/Passover recess in approximately 10 days, and the White House is both ready and willing to push back against legislation that administration officials believe would sabotage the talks or a final deal. If the general parameters outlined today can be fleshed out and if the outstanding gaps can be closed, then the president is in a strong position to make some headway on the Hill. He will face concerted congressional opposition almost irrespective of what the final deal looks like, but the framework shoud be significant enough to peel off just enough Democrats to avoid a veto-proof majority for the Corker bill, or alternatively to broker more amenable terms for congressional input into the negotiations themselves.

Ultimately, Congress has demonstrated more bark than bite on the Iran issue. Despite plenty of opportunity to take action on Iran since the November 2013 interim agreement, each time it has deferred. No one on the Hill wants to take ownership of the failure of diplomacy — or its relatively unpalatable alternatives, such as military action against Iran. That shouldn’t suggest that opponents of the deal will remain passive, particularly as domestic and regional concerns intensify about Iranian military interventions in Iraq, Syria and Yemen. As Galston highlighted in our discussion earlier this week, any future easing of pressure on Iran over its nuclear program is likely to be matched by more forceful American efforts to counter Iran’s regional policies.

The price of failure just increased

Finally, the administration has to contend with the reality that this latest success has only amplified the stakes for success in clinching a final deal. Despite the fact that a vast amount of work remains to be done to resolve the Iranian nuclear impasse, the framework announcement means that the Iran deal is now a done deal as far as the international community is concerned. If in fact negotiators cannot meet the June 30 deadline, or if the outstanding issues ultimately prove irreconcilable, then the president will likely face an even more imposing diplomatic challenge in reviving multilateral willingness to maintain pressure on Iran.

The pressure to make good on today’s promise should, in theory, apply even more powerfully to Iran, whose population is far more invested in a positive outcome to this process. News of the accord prompted spontaneous celebrations amidst late-night traffic in Tehran, and later Zarif received a hero’s welcome upon his return to the capital. Iranians are eager to see the trickle-down effects of a final deal, which promises a return to doing business as usual with the rest of the world and the beginning of the end of the country’s pariah status. That is precisely what opponents of the deal elsewhere in the region fear, but the prospect of such a rehabilitation poses a double-edged sword for Iran’s revolutionary regime. For all the regime’s recalcitrance, the Islamic Republic demonstrated this week that it cannot afford to walk away from a deal. That may prove the most powerful force to ensure the final bargain is struck and to sustain Tehran’s compliance with its terms.