Critics put Donald Trump on blast on Monday after he posted a message on social media threatening Iran with “Death, Fire and Fury.”

Writing on his Truth Social website, Trump said any attempt to block oil shipments would lead to an attack “TWENTY TIMES HARDER” ― and so severe that it will be “virtually impossible for Iran to ever be built back, as a Nation, again.”

Iran has responded to the U.S.-Israeli military campaign by threatening to attack ships passing through the Strait of Hormuz, effectively cutting off some 20% of the world’s oil. That’s triggered wild fluctuations in the market for crude oil, rising gas prices at U.S. pumps and fears of further economic pain should the conflict drag on.