By Zachary Keck, Special to CNN

Editor's note: Zachary Keck is managing editor of The Diplomat and a monthly columnist at The National Interest. You can follow him @ZacharyKeck. The views expressed are his own.

As the July 20 deadline for a deal over Iran's nuclear program approaches, it seems increasingly unlikely that Tehran and the P5+1 will reach a comprehensive agreement. Indeed, Iran has already signaled its willingness to extend the talks for another six months as outlined in the interim agreement, and President Barack Obama should therefore begin to prepare Congress for this reality as soon as possible. The U.S. has too much to lose by rejecting this offer. And fortunately for the administration, the case for extending the talks is an easy one to make.

To begin with, the U.S. has nothing to lose by agreeing to an extension. Despite the unconvincing arguments of its critics, the interim accord heavily favored the U.S. and its allies. Under the agreement, Iran agreed to freeze its nuclear program, as well as rollback its most dangerous elements. Equally important, Tehran agreed to intrusive inspections to demonstrate its compliance with the agreement.

In return, Iran received roughly $7 billion in sanctions relief spread across the six month period. At the same time, the P5+1 refused to lift the sanctions regime, which costs Iran an estimated $5 billion per month. Iran therefore continues to lose billions of dollars every month the negotiations drag on. All this means that even if extending the talks doesn't result in a comprehensive agreement, it will still freeze Iran's nuclear program and continue to squeeze it economically.

By contrast, refusing to extend the talks would allow Iran to restart its nuclear program immediately, likely at an accelerated pace, while also empowering Iran on the world stage by isolating the U.S. from most of the international community. This would be a major win for Iran. In fact, it may even be the goal of some within the Iranian leadership. When President Hassan Rouhani led Iran's nuclear negotiating team in 2003-2005, Tehran entered into talks with the EU+3 (France, Britain, and Germany). According to Rouhani's spokesperson at the time, Iran hoped these talks would divide the U.S. and Europe on the nuclear issue, thereby reducing the pressure Iran faced.

Similarly, Iran's rejection of the Obama administration's fuel-swap proposal in 2009 is what created an international environment that made imposing the current sanctions possible. Refusing Iran's offer to extend the talks would jeopardize these sanctions. China and Russia, meanwhile, have already signaled they will strengthen economic ties with Iran if the U.S. undermines the negotiations, an example that would likely quickly be followed by rising powers like India, South Africa and Turkey, and possibly even U.S. allies like Japan and South Korea, all of whom have significant interests in Iran.

Most importantly, though, America's refusal to extend the talks would no doubt prompt important European countries with strong interests in Iran, such as Italy and Germany, to push the EU to remove their own sanctions. Thus, ending the talks would allow Iran to resume its nuclear program even as it reduced the economic pressure it faces.

Rejecting an extension would also empower Iran's hardliners domestically. The current Rouhani administration has based much of its pitch for public support on the outcome of the nuclear talks. While Iranian Supreme Leader Ali Khamenei has cautiously backed Rouhani's diplomacy, he has distanced himself from the outcome of talks. With this in mind, America's refusal to even extend the talks would validate the hardliners' argument that the U.S. wants to prolong the nuclear crisis in order to justify continued sanctions. The Supreme Leader would have no choice but to back these hardliners, giving them the political capital necessary to accelerate the nuclear program, as well as harden Iran's position on other crucial issues like Syria.

But perhaps most important, the U.S. should extend the talks because a comprehensive agreement is still possible, and remains the best option for preventing a nuclear-armed Iran. Trying to solve the decade-long nuclear crisis in six months was always an overly ambitious goal. As such, failure to meet this deadline in no way proves Iran's insincerity.

The Syrian chemical weapons deal is instructive. That agreement also set an overly ambitious timeline for removing all of Syria's chemical weapons. But although plenty of deadlines were missed, Syria ultimately relinquished all of its declared chemical weapon stockpiles. This is far more than U.S. airstrikes could've hoped to accomplish. Even Israel Prime Minister Benjamin Netanyahu praised the Syrian agreement as "one ray of light in a very dark region."

The same possibilities exist for Iran's nuclear program if the talks are extended. But even if a comprehensive agreement isn't reached, continuing the negotiations would still benefit the U.S. and its allies. Ending them prematurely serve only Iran's interests.​