This week, the U.S. has a chance to lead an international coalition into an agreement that would guard against any attempt by Iran to obtain a nuclear weapon. However, the decades since the Iranian Revolution in 1979 are littered with missed opportunities to resolve differences between the U.S. and Iran, including on the nuclear issue. With political capital expended to keep the negotiations afloat, particularly in Washington, and the list of issues to be resolved shrinking, these negotiations have steadily risen in importance. As a result, failure or the rash rejection of a breakthrough by Congress or Iranian hardliners could result in irreparable damage to the diplomatic track, with profound consequences for an already chaotic region.

We may never see a pair of U.S. and Iranian Presidents more willing to expend the political capital necessary to reach a nuclear deal. President Obama famously distinguished himself on the campaign trail in 2008 by vowing to sit down with any world leader without preconditions, including Iran, and has turned an Iran nuclear deal into what could be the chief foreign policy goal of his second term. Secretary of State John Kerry and other top U.S. diplomats have also spent countless hours doggedly pursuing a deal that balances between the political imperatives of Washington and Tehran.

In Iran, President Rouhani campaigned on a platform of moderation and outreach to the West. Rouhani was the lead nuclear negotiator for Iran between 2003-2005, which resulted in Iran freezing its enrichment and implementing the IAEA’s Additional Protocol. Rouhani’s foreign minister, Mohammad Javad Zarif, also has a successful track record of negotiating with the West, playing a critical role in the effort to form a new government for Afghanistan at the Bonn conference in 2001. Over the past year and a half of intense negotiations, Rouhani and Zarif have kept Iran’s skeptical Supreme Leader united behind their efforts to reach a deal, preventing counterproductive divides in Iran’s political elite.

Now, with the political scales tilted heavily in favor of diplomacy, failure could eliminate diplomatic prospects for the foreseeable future. Escalation will be the name of the game if negotiations fail, as lead U.S. negotiator Wendy Sherman articulated in October. Congress would pass sanctions and President Obama might not put up much of a fight. Iran would expand its nuclear program and limit the access of international inspectors. The sanctions regime would fray or potentially collapse, diminishing U.S. leverage over Iran. Tacit cooperation in Iraq to counter ISIS militants could end, with dangerous consequences.

If diplomacy fails, President Obama would likely resist the reinvigorated calls from neoconservative circles to attack Iran, but he has less than two years remaining in office. Prominent Republicans weighing Presidential runs have already staked out a hardline position by warning Iran that they would undo any potential multilateral nuclear agreement “with the stroke of a pen.” Democrats, as well, could be scarred by failure and rush toward a hawkish position. Whereas a multilateral agreement would constrain the next President from returning to the escalation route, an advancing Iranian nuclear program and the lack of diplomatic prospects would tempt many of Obama’s potential successors to consider the military option, regardless of the consequences. Those who have dreamed of attacking Tehran ever since the fall of Baghdad are banking on such an opportunity to renew their case for yet another disastrous war.

It has been ten years since the European 3 (the United Kingdom, France and Germany) had a golden opportunity to constrain Iran’s nuclear program. Those talks fell apart largely due to the George W. Bush administration’s insistence that any agreement result in Iran eliminating its entire centrifuge program. As a result, Iran went from hundreds to 20,000 centrifuges as economic pressure escalated but failed to achieve any strategic goal. Now, diplomacy has once again halted the Iranian program’s advance and could lead to a historic breakthrough that reshapes the U.S.-Iran relationship, cuts off Iran’s pathways to a nuclear weapon and averts a disastrous war. If an agreement falls through, however, getting through another ten years without a war, an Iranian nuclear weapon, or both would likely prove more challenging than reaching the diplomatic inflection point that the parties now face in Lausanne.

This piece was originally featured in The Huffington Post.