If there is one place in the world where the difference of opinion between Europe and the USA over how to deal with Iran will be most glaringly apparent, it will be in Tehran this Saturday. That is where Iran's re-elected president, Hassan Rouhani, will take the oath of office for his second term. EU High Representative for Foreign Affairs Federica Mogherini and French Foreign Minister Jean-Yves Le Drian will be among the guests at the ceremony. Germany will be represented by a deputy foreign minister.

Their appearance will stand in stark contrast to the attitude of the United States. Speaking in Saudi Arabia in May on his first foreign trip, US President Donald Trump said, "all nations of conscience must work together to isolate Iran." The attitude signals a serious threat to the so-called Iran nuclear deal signed just two years ago.

The Joint Comprehensive Plan of Action (JCPOA) agreement to contain Iran's nuclear activities was the basis for that country's return to the international stage and its reintegration into the global economic system after years of harsh sanctions. The core of the nuclear deal: Iran commits to rolling back parts of its nuclear program, as well as allowing regular inspections thereof, and in return, related sanctions will be suspended and eventually lifted altogether.

So far, the agreement has worked. In six consecutive reports, the International Atomic Energy Agency (IAEA) has certified that Iran is upholding its end of the bargain. Therefore, the EU sees the nuclear deal as a major step toward making the world safer and stopping nuclear proliferation.

Two years ago the nuclear agreement was celebrated on the streets of Tehran

Read more: Iran vows to continue missile program as tensions flare with US

'Majority wants to derail the nuclear deal'

The mood in the USA couldn't be more different. Sascha Lohmann, from the Berlin-based German Institute for International and Security Affairs (SWP), told DW that both the president and Congress are skeptical about the deal. "A broad majority is in favor of scrapping the deal or trying to renegotiate a better one. That means there is a great danger that things may soon change on the US end of the agreement in the very near future," says Lohmann.

The next opportunity to initiate such a change will come in October. The US president is obliged to inform Congress whether or not Iran is continuing to uphold the agreement every 90 days so that the body can decide whether or not to extend sanctions relief. Trump has already done so twice, albeit with discernible reluctance – and with obvious displeasure over the approach of his own State Department. Meanwhile, the White House has assembled its own working group on Iran – tasked with finding a way for Trump to impose new nuclear-related sanctions on the Islamic Republic.

Ali Vaez told DW that this fact leads him to fear that the Iran nuclear deal is in grave danger. An Iran expert from the International Crisis Group, Vaez says it is more than media reports claiming President Trump promises to refuse certifying Iranian compliance in October that concern him. When speaking with DW he added: "US government officials are openly calling for regime change in Iran." This also fits with Wall Street Journal (WSJ) reports that CIA Director Mike Pompeo has set up a special Iran Mission Center.

The Iran Mission Center, a new department within the CIA, should put greater pressure on Iran

'If they don't let us in, boom'

In its article, the WSJ quoted anonymous US officials who said the CIA's activities mirrored the Trump administration's prioritization of Iran as a target for US agents. Pompeo has been a hawk on Iran for years and has harshly criticized the nuclear deal in the past.

But the deal is working as far as Republican Senator Bob Corker of Tennessee is concerned. Corker, who chairs the Senate Foreign Relations Committee, has lobbied against derailing the agreement. But his true intentions became clear in a recent interview with David Ignatius of the Washington Post (WaPo). "What you want is you want the breakup of this deal to be about Iran. You don't want it to be about the United States," said Corker. He also called for "radically enforcing" the agreement, for instance by demanding access to "various facilities in Iran. If they don't let us in, boom."

Sword dance and tweets

European allies, on the other hand, have shown no intention of following the US's lead. For Rolf Mützenich, chairman of the German-Iranian parliamentary group in Germany's lower house, the Bundestag, the presence of European foreign policy representatives at Rouhani's inauguration sends a clear signal that Europe "intends to maintain its contract-based agreement with Iran." At the same time it sends the message that, "we want to continue to work in trusting cooperation with President Rouhani." In Mützenich's opinion that is important because he sees Rouhani as a guarantor for Iran opening itself to the world – "unlike other actors in Iran."

EU High Representative Mogherini is relentless in her promotion of the nuclear deal as well: She was the first foreign politician to congratulate Rouhani on his election victory, via Twitter – and at the same time she used the opportunity to emphasize European willingness to work toward accomplishing the aims of the agreement.

'EU companies aren't regulated in Brussels but rather in Washington'

Should the USA actually break away from the JCPAO it would have far-reaching consequences – even if other partners stuck with it. Those partners are the EU, Germany, France, the UK, China and Russia. The economic exchange that has finally been reignited could suffer greatly, as so-called secondary sanctions could hit European companies doing business with Iran. SWP Iran-expert Lohmann was very clear when speaking with DW: "We are faced with the problem that EU companies are not actually being regulated by Brussels, but rather by Washington. That is why big companies have openly said: US sanctions are the determining factor for us. Even if we have no legal consequences to fear from the European side, we still won't do business with Iran. We are too scared of violating US sanctions."