As President, Donald Trump has always had the power to blow up the Iran nuclear deal for any reason or no reason at all.

On Friday, he sought to foist that responsibility on the US Congress but the decision ultimately remains with him.

His announcement that he was “de-certifying” the Joint Comprehensive Plan of Action (JCPOA) deepens the concern over US policy toward Iran that has been there since his inauguration. The most important question now is not what Trump or Congress will do but how Iran and the rest of the world will respond.

Early indications are that the other signatories to the pact will stand firm in support of the agreement, which was laboriously negotiated over more than a decade.

The European Union and leaders of the E-3 – Britain, France and Germany – which played a pivotal role in initiating negotiations with Iran, have sought unsuccessfully for months to convince Trump of the merits of the JCPOA. They will now pivot and refocus even more of their attention on Congress in hopes of averting deal-busting legislation – and on Tehran to encourage Iran to continue to comply with the deal’s nuclear requirements.

Emmanuel Macron has already signaled his desire to become the first French president to visit Iran since the 1979 revolution, while the EU’s foreign policy chief Federica Mogherini plans to travel to Washington in November.

Burdened with thorny domestic issues, Congress may well do nothing on Iran – in which case the decision returns to Trump. While the certification question is purely a US domestic matter, under the JCPOA, the president must waive nuclear-related sanctions every six months. The next deadline comes in 2018.

As the US and Europe weigh their options, Iran is so far taking the high road. In a lengthy statement issued after Trump spoke, the Iranian government defended the JCPOA as “a valid international instrument and an outstanding achievement in contemporary diplomacy” that “cannot be renegotiated or altered.” But the Iranians also made clear that if their “rights and interests … are not respected,” they could resume their “peaceful nuclear program without any restrictions.”

In signing the agreement, Iran’s national security establishment concluded that the value of sanctions relief outweighed the intrusions on Iranian sovereignty entailed in accepting temporary nation-specific limits on nuclear activities beyond those required by the nuclear Non-Proliferation Treaty. Iranian leaders will continue to perform a cost-benefit analysis to determine whether it is worth it to remain within the JCPOA.

Here, the actions of foreign businesses looking to invest in Iran will have more impact than the declarations of foreign leaders.

At a conference in Zurich earlier this month that brought together prominent officials and business executives from Iran and Europe, representatives of major European firms said they would continue to invest in Iran but that US hostility toward the JCPOA would make it even harder to obtain necessary financing. A resumption of US secondary sanctions would certainly exacerbate those difficulties.

The executives also spoke of continuing obstacles within Iran to trade and investment that are partly but not entirely the legacy of sanctions. Among them: difficulty identifying the ownership structure of Iranian counterparts, including banks; myriad regulations that make labor cost 30 percent more in Iran than in India; chronic corruption; and continued domination of many sectors of the economy by state-owned enterprises.

Iran, which says it needs $50 billion in foreign direct investment over the next five years to reach its goals for economic growth and job creation, could also significantly increase its attractiveness for foreign capital if it released the dozen or so dual nationals it has jailed on bogus charges of espionage – including 81-year-old former UNICEF official Baquer Namazi and his son, Siamak, who on Sunday spent his 45^th birthday in Evin prison. While President Trump in many respects hyped the case against the Islamic Republic in his bellicose speech, he was absolutely right to point out that Iran continues to imprison Americans “on false charges.”

Unfortunately, by undermining the one area where Iran is in full compliance with its international obligations, Trump has handed a major propaganda victory to the most hardline elements in the Islamic Republic – those responsible for seizing dual nationals, repressing Iranian civil society and intervening on the side of murderous dictators such as Syria’s Bashar al-Assad. Already, one can see a “rallying around the flag” by Iranian officials and ordinary Iranians in support of the Islamic Revolutionary Guard Corps, which the Trump administration slapped with new sanctions last week.

Iran now feels more justified in calling the United States a “rogue regime” and reminding the world of the chaos and misery ill-conceived US policies toward the Middle East have historically unleashed. While the US case against Iran always starts with the 1979-81 hostage crisis, the Iranian version invariably begins with the US overthrow of Iranian Prime Minister Mohammad Mossadegh in 1953, followed by US support of Iraq’s Saddam Hussein in the bloody Iran-Iraq war of the 1980s.

The main cause of Iran’s regional rise was the US overthrow of Saddam in 2003 on false charges of possessing weapons of mass destruction. That war also created Al Qaeda in Iraq, the precursor to the Islamic State group, which has carried out savage attacks on Iranians as well as Americans, Europeans, Arabs, South Asians and Kurds.

Given his frequently expressed dislike of “nation-building” and massive US military interventions abroad, Trump is unlikely to fulfill his other promise to counter Iran’s regional interventions. Because of the relative weakness of US allies in the region despite massive US arms sales – and the still festering dispute within the Gulf Cooperation Council between Saudi Arabia and Qatar – Iran is likely to continue to gain influence in Lebanon, Syria, Iraq and Yemen at the expense of the US and its friends.

A more prudent US strategy would be to use the direct channel with Iran afforded by the JCPOA to discuss how to resolve regional conflicts and avoid an accidental clash between US and Iranian forces in the narrow body of water that Trump incorrectly — and insultingly to all Iranians — called the “Arabian” Gulf.

But that would require the sort of diplomatic depth and bureaucratic consistency that the Trump administration has failed to demonstrate nine months into its tenure. As with so many other crucial issues, from health care to climate change, Trump seems to find it both easier and more personally satisfying to dismantle the achievements of his predecessor than to build on them.

Barbara Slavin is director of the Future of Iran Initiative at the Atlantic Council.