Europe’s three biggest powers—Britain, France, and Germany—have triggered a dispute mechanism over the nuclear deal with Iran. It’s the strongest indication yet that the Europeans may follow the U.S. lead in abandoning the deal. Since President Donald Trump pulled the U.S. out of the accord two years ago, European allies have attempted to stop it from collapsing entirely. But, since the U.S. withdrawal, Iran has gradually exceeded many of the limitations it agreed to in the deal, including abandoning limits on its production of enriched uranium. Those breaks with the deal have forced the European powers to respond. Under the triggered mechanism, there will be 15 days to resolve the differences. If that fails, it could ultimately lead to the reimposition of sanctions that were in place under previous UN resolutions before the agreement. Earlier Tuesday, U.K. Prime Minister Boris Johnson said the way forward was to agree to a “Trump deal” to replace the 2015 deal struck by President Obama.