It is called the “Trump effect,” and its ripples are already being felt across the Middle East. Iran, which for weeks had been threatening to retaliate against Israel for its own retaliatory strikes recently on Iranian targets, has noticeably toned down its rhetoric and seems to have recalibrated to the point that is even making overtures to the incoming president.

Iran’s ambassador to the United Nations met with businessman Elon Musk, a close supporter and confidant of Donald Trump and, at the same time, ceasefire talks between Israel and Hezbollah – Iran’s most important proxy – have significantly ramped up. In addition, the head of the International Atomic Energy Agency made a rare visit to Iran this week, for the first in time in more than six months.

Iran’s new-found caution is not without good reason. Trump’s previous term in office was marked by policies that deeply rattled the regime. He withdrew the US from the Iran nuclear deal – formally known as the Joint Comprehensive Plan of Action (JCPOA), he imposed harsh sanctions and he ordered the killing of Qasem Soleimani, the iconic commander of the Islamic Revolutionary Guard Corps’ (IRGC) elite Quds Force.

What has also got Iran’s attention are Trump’s personnel choices. Representative Michael Waltz of Florida, tapped to serve as Trump’s national security adviser, is one of the most hawkish American politicians when it comes to Iran. Last month, after Israel responded to an Iranian ballistic missile attack, Waltz said that he actually supported Israel doing more. “This might be Israel’s last best chance to diminish Iran’s nuclear programme and shut down their cash,” Waltz declared in a tweet, suggesting Israel should have targeted key oil infrastructure and Natanz, one of Iran’s key nuclear facilities. “Did Biden/Harris pressure Israel once again to do less than it should?”

Florida senator Marco Rubio, Trump’s nominee for secretary of state, is equally unyielding when it comes to Iran. After Iran attacked Israel on October 1, Rubio tweeted: “Iran’s regime wants to destroy Israel so they can become the dominant power in the Middle East. Appeasement will not change their behaviour. Only threatening the survival of the regime through maximum pressure and direct and disproportionate measures has a chance to influence and alter their criminal activities.” Other prominent Trump allies have echoed this hardline approach. Senator Tom Cotton of Arkansas urged the US to support Israel “to the hilt to destroy our common enemies”. Similarly, Brian Hook, a former special envoy for Iran and now overseeing the State Department transition for Trump, said he expects Israel to strike Iran decisively to shift “the balance of power in the region”. In Hook’s words, Israel “can” and “should” take such action.

Trump’s history and his appointments make it clear that his administration will pursue a tough line against Tehran. The critical question is how far is Trump willing to go?

During his first term, Trump’s administration hoped that withdrawing from the JCPOA and imposing “maximum pressure” sanctions would force Iran back to the negotiating table. The goal was to use the talks to reach a new deal – one that Trump could tout as “stronger” and “longer” than the one brokered by his predecessor, Barack Obama. That gamble didn’t work and Iran opted to wait Trump out. After the 2020 election brought Joe Biden to power, US policy shifted back to seeking diplomacy with Tehran.

Although Iran rejected Biden’s overtures, the Islamic Republic still benefited from a more lenient approach. Some sanctions relief was provided and the pressure on Tehran diminished to the extent that the regime no longer felt seriously threatened.

Now, with Trump returning to office, reports suggest he is already preparing executive orders to reimpose crippling sanctions on Iran, particularly targeting oil exports.

These orders, which might come on his first day in office, aim to strangle Iran’s economy, cutting off funding for terrorist groups such as Hamas, Hezbollah and the Houthis, while hindering its nuclear ambitions.

But sanctions alone won’t suffice. For any strategy to succeed, it must be paired with a credible American military threat. This can be done by amassing military forces in the region and delivering a clear, unequivocal warning from the Oval Office.

Trump has demonstrated that he understands the value of military force. His decision to eliminate Soleimani in January 2020 is a prime example.

At the time, Iran’s proxies were routinely attacking US targets. After Soleimani’s death, those attacks dropped dramatically. The message was clear: the US was willing to act decisively – and Iran took notice.

Without a credible military threat, Iran has little incentive to change its behaviour. Until Israel’s retaliation last month, the regime in Tehran operated with a sense of impunity, arming its proxies and advancing its nuclear programme without consequences. That mindset needs to be dismantled.

History shows that military deterrence is possible. In 2003, as the US prepared to invade Iraq, Iran – fearing it might be next – suspended its nuclear programme. What this showed was that when faced with the dilemma, Iran’s leadership prioritised survival over its nuclear ambitions and its support for terrorist proxies.

This pattern of behaviour is why Iran is hesitating now to use force against Israel and why it is green-lighting a potential ceasefire between Israel and Hezbollah in Lebanon.

It is doing all of this because it is concerned what might happen when Trump takes office. That is leverage that Trump needs to continue to capitalise on to stop Iran. It is an historic window of opportunity that the world cannot afford to miss.