The missiles that struck last weekend in Saudi Arabia did not just destroy oil tanks. They also dealt the final blow to a doctrine that has been fading for years: the belief that the United States maintains a security umbrella able to protect the oil-rich Persian Gulf states from their enemies — and, especially, from Iran.

President Trump’s miscalculations helped get us here. But the current Gulf crisis is not just about this administration and the pitfalls of its “maximum pressure” campaign against Iran. The United States has been disengaging from the Middle East since the catastrophe of the 2003 Iraq invasion. Now that shale has made America so much less dependent on the Middle East’s oil, it is hard to imagine any American president risking significant blood and treasure to defend Saudi Arabia.

For decades, the leaders of the Gulf seemed to believe their close ties with the United States (and the billions of dollars spent on American weapons) made them almost invulnerable. They regularly urged American diplomats and generals to get tougher with their Iranian neighbor or even to “cut off the head of the snake,” as Saudi Arabia’s King Abdullah put it in 2008 in encouraging the United States to bomb Iran’s nuclear sites. Saudi confidence was bolstered by memories of the 1991 Gulf war, when an American-led military coalition reversed Saddam Hussein’s invasion of Kuwait.

But the faith in American power always blinked away some inconvenient facts. Iran’s population and military strength dwarf those of the Gulf countries, and the United States is nearly 10,000 miles away. In any conceivable war, the Gulf’s cities would be among the first targets. And unlike Iran, those cities are intensely vulnerable: A single bomb could shatter the status of Dubai as a safe hub for trade, transport and tourism.