Reza Marashi is research director at the National Iranian American Council. Trita Parsi is the president of the council and author of the forthcoming book, "Losing an Enemy -- Obama, Iran and the Triumph of Diplomacy." (Yale University Press, 2017)

(CNN) As Donald Trump prepares to enter the White House , he will be the latest in a long line of Presidents to inherit Middle East security challenges.

It lies in the interest of the United States to build on the Iran nuclear deal to resolve remaining tensions with Iran and help stabilize the Middle East. The nuclear deal itself was a significant contribution to regional security. Both the risk of an Iranian nuclear bomb and a military confrontation with Iran have been significantly reduced. But Trump must now go even further.

A new report, published this week by the National Iranian American Council and signed by 76 national security experts, argues that Trump should take the political risk necessary to broaden the opening to Iran precisely to avoid replicating recent US policy failures in the Middle East.

This is critical in order to achieve what Trump has listed as one of his priorities: defeating ISIS. Indeed, even if President-elect Trump views the Iran deal negatively, he has to choose between fighting ISIS or scuttling the Iran deal. He cannot do both.

Mindful of Iran's role in fighting ISIS -- which Trump publicly acknowledges -- he cannot walk away or renegotiate the nuclear deal without undermining the coalition against the terror group.

Trump has indicated a departure from Obama's calls for Iran and Saudi Arabia to share the balance of power in the Middle East. His top national security adviser, Michael Flynn, has called for regime change in Iran and spoken out forcefully against the nuclear deal.

Rhetoric, however, is not preordained to become reality. Policy preferences can change when a new President enters office.

To that end, if diplomacy could be successful in resolving the most volatile and complex point of tension between the US and Iran -- the nuclear dispute -- Trump should also employ diplomacy to peacefully resolve the remaining differences between Washington and Tehran.

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Undoubtedly, this is not a simple proposition. Iran's willingness and ability to engage the US on regional matters has not yet been fully tested. But what remains unquestionable is that it lies in the interest of the US to better manage its ties with Iran so that the two countries have a functional relationship. A quick glance at the geopolitical chessboard demonstrates this necessity.

Iran has substantial latent power -- population size and potential for wealth generation -- and thus it is bound to be a leading power in the Middle East. Washington cannot change this. Nor can Washington stabilize the Middle East without Iran's involvement..

In our report, we provide policy recommendations for eight different dimensions of the US-Iran relationship and flesh out how American national interests can be advanced through concrete short- and long-term measures: from the bilateral relationship with Iran, to the Saudi-Iran rivalry, to the stabilization of Iraq and Afghanistan, to ending the Syrian civil war, to sanctions relief and human rights in Iran.

The linchpin of regional stability in this new era -- be it Syria, Iraq, Afghanistan, or elsewhere -- is ending the Saudi-Iran cold war. Therefore, Trump should directly communicate to Saudi Arabia and Iran that it is in the US national interest to avoid taking sides in aspects of their rivalry in which its own interests are not at stake -- and that it favors détente and rapprochement between the two.

To that end, the US should encourage Riyadh and Tehran to implement military confidence-building measures in the Persian Gulf; carry out a shared strategy for destroying ISIS; restart Sunni-Shia dialogue to reduce sectarianism and promote tolerance; and urge both sides to conclude an appropriate non-aggression pact.

The nuclear deal proved that it is possible to change long-contentious aspects of our relationship with Iran using tough-minded diplomacy. The US and Iran may not become the best of friends anytime soon, but they no longer need to be the worst of enemies. Problems will persist, but not to the extent that it requires overlooking or ignoring the substantial number of overlapping interests.

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If Trump squanders this opportunity, the dangers facing America are very real. It will increase the likelihood that the Iran deal collapses, which in turn will lead to Tehran reversing the limitations it made to its nuclear program and escalating its nuclear activities. An Iranian nuclear option will become a near-certainty.

Washington has reiterated countless times its willingness to go to war to stop an Iranian bomb. Eliminating Iran's nuclear program, however, will require a US invasion and occupation of Iran. This sobering reality is what led Barack Obama to wisely pursue diplomacy with Iran in the first place.

We now know that diplomacy can bear fruit, despite skepticism about Iranian sincerity and the willingness of Iran's leadership to abide by diplomatic agreements. Therefore, Trump should continue transforming US-Iran relations over time and allow the two countries to collaborate when their interests coincide.

The common fight against ISIS is an obvious starting point.