This week’s events at and surrounding the UN General Assembly will help determine whether the U.S. and Iran can resolve their differences, or if hardliners on either side will once again succeed in sabotaging reconciliation.

Iran’s new President, Hassan Rouhani, has arrived in New York seven weeks into his presidency at what could be the apex of his electoral honeymoon. He has received the endorsement of the Supreme Leader to negotiate with “heroic flexibility” in forthcoming nuclear talks, succeeded in wresting control of negotiations from Iran’s security establishment, exchanged letters with President Obama, and obtained the release of approximately 90 political prisoners ahead of his New York visit, including human rights advocate Nasrin Sotoudeh. Later this week, Rouhani’s new Foreign Minister, Mohammad Javad Zarif, will sit down with Secretary of State John Kerry and the other chief diplomats of the P5+1 (the five permanent members of the UN Security Council plus Germany) for the highest-level diplomatic talks since Iran’s 1979 Revolution. By moving talks up to the ministerial level, this week’s talks are likely to infuse diplomatic clout and urgency that has been lacking in previous negotiating rounds.

But honeymoons do not last. Rouhani has spent political capital on a “charm offensive” with the West, including an interview with NBC’s Ann Curry in which he disavowed the pursuit of nuclear weapons and an op-ed in The Washington Post. If he fails to deliver results in the form of sanctions relief, hardliners within Iran who distrust his conciliatory approach will move to block chances for a nuclear deal. That is why Rouhani has insisted that the time for resolving the nuclear impasse is limited.

Rouhani has firsthand experience with this dynamic as the lead nuclear negotiator for President Khatami. In 2003, Rouhani struck a confidence building deal with the European 3 (the UK, France and Germany) to suspend enrichment and adopt the IAEA’s Additional Protocol, allowing for enhanced transparency over Iran’s nuclear program. However, when these steps failed to lead to reciprocal concessions from the West, Rouhani and Khatami were branded appeasers and the ideological Mahmoud Ahmadinejad reversed their gains and embarked on eight years of amplifying tensions with the West. If we fail to capitalize on the opening before us, we risk repeating those same mistakes.

Obstacles to a deal are at least as difficult within the United States as inside Iran. Congress is set to consider a number of hostile actions that could sabotage renewed hopes for diplomacy. After the House passed a sanctions bill that would impose a virtual embargo on Iran mere days before Rouhani’s inauguration, the Senate is set to consider a companion bill in the weeks ahead. And, having failed to authorize military force against Syria, Rep.Trent Franks (R-AZ) and Sen. Lindsey Graham (R-SC) are implementing plans to introduce a war resolution against Iran. While these counterproductive measures were an easier sell before Rouhani’s inauguration (the hawkish Rep. Ileana Ros-Lehtinen (R-FL) has already declared, “I miss Ahmadinejad“), there is still significant political support in the halls of Congress for renewed sanctions and escalating military threats against Iran.

Apart from Congressional action, President Benjamin Netanyahu and his fellow Iran war hawks are pushing a hardline stance that would render nuclear talks pointless. According to Netanyahu, Iran should be forced to abandon its entire nuclear program by halting enrichment and dismantling its nuclear facilities and centrifuges. In essence, Netanyahu’s stance is unyielding coercion, not diplomacy. Such a policy would set us on the path to war, which would make an Iranian nuclear weapon more, not less likely, given the inability of airstrikes to erase Iran’s nuclear know-how and the certainty that Iran would pursue a nuclear weapon to deter future strikes.

In spite of the pressure campaign against Iran, which has played into the Iranian hardliners’ belief that the United States is interested in regime change and not diplomacy, Rouhani’s election has presented us with another opportunity to resolve the nuclear impasse. But each side will need to invest significant political capital to head off hardliners and strike a nuclear deal while the iron is hot. For Rouhani, the longer he can hold the diplomatic window open, the greater the likelihood that he can deliver on his campaign promises. This will take deft maneuvering and even more political capital to satisfy the right people within Iran’s political establishment. But the success of his presidency is intrinsically tied to rapid success on the nuclear issue. On the American side, success means putting significant sanctions relief on the table immediately — including on oil and financial sanctions, clarifying the endgame with Iran, and taking immediate action to reciprocate Rouhani’s flexible stance. For example, the Obama administration’s lifting of sanctions on humanitarian work and sports exchanges with Iran should be followed up with additional measures to ease the plight of sanctions on Iranians.

This week could represent a fundamental change in the course of U.S.-Iran relations. Or it could represent a point of no return, a missed opportunity on the path toward war when leaders overlooked a critical opportunity to shift relations in a positive course. Let’s hope they take advantage of this critical moment.

(This article originally appeared on Huffington Post)