US President Donald Trump brands himself as a dealmaker but arguably, the most significant American deal struck in the past 40 years since Camp David, was the Iran Nuclear Agreement by former President Barack Obama. Achieving with a sweep of the pen what years of "debilitating" sanctions never accomplished, the Joint Comprehensive Plan of Action (JCPOA) stilled Iran's uranium enrichment programme and reduced its nuclear stockpile.

Yet Trump has called it the “worst deal ever negotiated” and vowed to “tear it up”. Trump’s electoral bluster against the Iran deal could be diffused by workaday reality. He remains positive toward Moscow – and President Vladimir Putin's most significant ally in the Syrian war theatre is Iran. What is more, Iran is actively fighting the Islamic State of Iraq and the Levant (ISIL), which Trump really hates.

Significantly, the hardest-nosed, anti-deal hawks – including Newt Gingrich and Rudy Giuliani – failed to secure seats in Trump's cabinet. Instead, newly appointed Defense Secretary General James Mattis has stated that to scupper it would sully Washington's trustworthy image, and isolate the US, as allies in the European Union and United Nations would be unlikely to follow suit.

Yet, Trump may still see compelling reasons to rip it up. First, he, like Hillary Clinton, is much more favourable towards Israel than Obama was, and Israel is starkly anti-Iran and hates the JCPOA.

Second, the prospects for US business in Iran remain slim, while opportunities with Saudi Arabia and other conservative Arab regimes are vibrant. As Riyadh is embroiled in its own soft war with Iran, while anxious to maintain cosy relations with Washington, encouraging Trump to rip up the deal is a Kingdom goal.

Third, the deal's future is vulnerable not only in Washington but also in Iran, where hardliners never strongly supported it, and where a political standoff between reformers and hawks is taking shape in the run-up to the presidential elections of April 2017. This uncertainty has been exacerbated by the death of pragmatist reformer Hashemi Rafsanjani, which has left President Hassan Rouhani fighting for his future, and the deal.

The consequences of scrapping the JCPOA would be dire - Iran's nuclear re-activation, a possible regional nuclear race and an escalation of conflict in the neighbourhood.

Ali Akbar Salehi, the head of Iran's Atomic Energy Organization, has hinted that Iran could regain most of its enrichment capability within a year and a half.

Tehran, however, would have to decide whether it, too, would rip up the deal and lose its economic windfall. If Iran's hardliners prevail and it backs out of the JCPOA, business deals with the EU would abruptly be cut off. The oil and gas industries - the biggest beneficiaries of post-sanctions investment - would shrink, plunging Iran into a new recession, dashing the hopes of its vast youth population, prompting possible domestic unrest and likely clampdowns.

With the prospect of closer US-Iran relations no longer containing Saudi ire against Iran, the chances of growing conflict between these two Gulf powers could be expected to rise, an unprecedented situation in modern regional history, as until now, they have never allowed their simmering mistrust and Sunni-Shia competition to boil over into outright war.

Finally, a cancelled deal would mean no more inspections of Iran's nuclear programme. This combined with an Iranian missile programme that is expanding rapidly, makes a toxic combination, one that could attract an Israeli "corrective" attack with Trump support, immediately broadening the turmoil in the Syria-Iraq theatre into a wider and highly militarised regional war.

The JCPOA is a compromise that has worked. Getting more guarantees for the US would mean forcing Iran to accept more concessions, which its hardliners won't do. Though Trump may be a great deal maker, Obama's Iran deal is about as good as it gets. (Roxane Farmanfarmaian/Al Jazeera)

•Roxane Farmanfarmaian is an Affiliated Lecturer in International Relations of the Middle East and North Africa at University of Cambridge.

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