Corporate Europe is bowing to the pressure of Washington’s unilateral sanctions on Iran. The continent’s leading multinational firms, such as Airbus, Maersk, Peugeot, Total, and Siemens, are leaving a market many of them entered with enthusiasm after the 2015 nuclear deal with Iran.

The trickle of departures since Washington’s withdrawal from the nuclear deal has made it difficult to appreciate just how dramatic the European divestment has been. To address that oversight, we have released a report that catalogs the efforts of 136 European companies to conduct business with Iran, including 38 firms whose annual revenues have earned them a place in the Fortune Global 500 rankings. (The study also examines almost 100 firms outside Europe.)

Our study identified 52 European firms that have clearly indicated they will cut ties with Iran. This includes 19 firms that are part of the Global 500. Since the full array of U.S. sanctions won’t return until Nov. 4, or 180 days after Washington’s withdrawal from the nuclear deal, many firms have kept quiet about their plans -- we placed 76 European firms in the “No Announcement” category. A mere six have said they will ignore Washington’s pressure, while two will continue to operate because they are covered by exemptions.

Remarkably, no European company in the Global 500 plans to defy sanctions. The one firm that tried, Renault­, soon chose to back down rather than put itself directly in the U.S. Treasury’s crosshairs.

For the French automaker, the cost of leaving Iran will be considerable. Last year, Renault signed the largest foreign auto deal in Iranian history, a $780 million agreement to increase its annual production capacity from 200,000 to 350,000 vehicles. In June, Renault announced its plans to resist.

Yet just six weeks later, the firm admitted it would likely put its Iranian operations on hold. It may seem strange that a firm which sells no cars in the United States would surrender a valuable market like Iran. However, what leading multinationals all understand is the potentially crippling risk of being cut off from the dollar and from the U.S. financial system.

Politicians on both sides of the Atlantic have had a more difficult time comprehending this fact. As part of their bid to save the nuclear deal, European governments have set up euro-denominated financing facilities to provide an alternative for firms dependent on the dollar. Companies’ interest was anemic. As a French official explained to Reuters, “When you’re an economic player and a multinational with interests in the United States that works in dollars, you have a choice and that choice is made quickly.”

The European Union also moved to activate a blocking statute that would theoretically forbid European firms from complying with U.S. sanctions. Yet the law cannot prevent the United States from cutting off their access to the dollar and to the world’s largest market.

Of course, the elected official who misjudged the power of unilateral sanctions most thoroughly was Barack Obama, who insisted that Washington would have minimal leverage in nuclear negotiations with Iran if the European Union lifted its sanctions. Thus, Obama explained in 2015, the United States had to make a deal quickly, lest the European Union grow tired of trying to isolate Iran.

In a sense, Donald Trump’s withdrawal from the nuclear deal represented a gamble that unilateral sanctions would be far more effective than his predecessor forecasted. If the United States withdrew and European firms ignored American threats, it would have exposed Washington as powerless and cemented the nuclear deal as the foundation of Iranian relations with the West.

Instead, Washington has shown its ability to put severe pressure on Tehran at a time when its currency is already collapsing and the Iranian people are protesting the corruption, mismanagement, and foreign wars that have left them increasingly impoverished. A little over a year ago, the rial was trading at 37,500 to the dollar. The regime has shut down the currency trade, but the dollar this week reached a high of 138,000 rial on the black market.

If Iran still refuses to accept tough and enduring restraints on its nuclear and missile programs, then the United States should campaign for Iran’s expulsion from SWIFT, the global financial messaging system that cut off Iran in 2012, condemning it to unprecedented financial isolation. This may lead to another showdown between Washington and Brussels, since SWIFT is a Belgian entity subject to EU law.

The odds still favor Washington, but the strongest message to Iran would come from a united U.S.-European front. This means the White House would have to temper its instinctive hostility to Europe, while Europe would have to acknowledge the deep flaws of the existing nuclear deal. Of course, the people of Iran may take matters into their own hands before Western leaders take action.

David Adesnik is director of research at the Foundation for Defense of Democracies, where Saeed Ghasseminejad is a fellow. Follow David on Twitter @adesnik and Saeed @sghasseminejad. The views expressed are the authors' own.