LAND WARS in Asia have rarely gone well for America. In Vietnam, Iraq and Afghanistan, America spent years on the ground, ensnared in conflicts for much longer than first expected. Now President Donald Trump is threatening to repeat the experience. Short of options to reopen the Strait of Hormuz, he has sent thousands of troops to the region and talked of invading Kharg Island, in the Gulf off Iran’s coast.

Kharg is appealing. It is a hub for 90% of Iran’s oil exports. Jimmy Carter and Ronald Reagan weighed attacking it; Saddam Hussein and Mr Trump bombed it. If America held the island, it would hope to deny Iran much of the 2.4m to 2.8m barrels of oil that it still exports daily. Iran earns more from those exports now than it did before the war began.

Marines and paratroopers could take the island. But then what? If they halted Iranian oil exports, energy prices would rise, further harming the global economy. Iran could attack more Gulf infrastructure, including vital desalination plants. America might also need to occupy three other terminals farther south—Jask, Lavan and Sirri—adding to the complexity of the operation. It would be far simpler to stop Iranian tankers at sea, as they left the Gulf.

American troops on Kharg would be exposed. They would need regular resupply by air or sea; Iran would attack runways or ships, and would rain drones and missiles on the occupiers. Kharg is near the Iranian mainland, putting it within reach of more Iranian missiles. Some would get through, as they have done in recent weeks, most recently destroying a valuable American E-3 Sentry airborne-radar aircraft in Saudi Arabia.

Alternatives would include seizing Iran’s smaller outlying islands, like Abu Musa and Greater and Lesser Tunb, or raids inland against military sites. But to be more than a nuisance America would have to stage long occupations, and these would probably run into the same problems as Kharg.

If the war becomes a contest of wills, Mr Trump should remember that the stakes are much higher for Iran’s regime. The loss of oil income, and other blows, could aggravate its economic crisis and perhaps trigger protests. But Iran’s regime is brutally repressive and has lived with a dysfunctional economy for years. Its willingness to endure pain vastly exceeds that of Mr Trump, whose party faces midterm elections in eight months. The Islamic Revolutionary Guard Corps bled American troops in Iraq with roadside bombs; they would relish doing so with projectiles.

America could stumble into a quagmire elsewhere. Mr Trump may favour a mission to seize Iran’s stock of 400kg of enriched uranium. Swooping into Isfahan, where the bulk of it is probably underground, would certainly be dramatic. It would also be the largest raid in military history. But some of the uranium is probably held beneath the ground at two other sites, Natanz and Fordow. Assaulting three places at once may be beyond even America’s capabilities.

Americans are not the only ones who should worry: so should their allies. The war is already sapping American military power. The destroyed E-3 Sentry was one of a small and shrinking fleet. America has fired over 850 Tomahawk missiles, more than it expended in Iraq in 2003, perhaps a third of its available global stocks. The intense pressure on American ships is likely to compound a maintenance crisis in the navy. American and allied planners in the Pacific will be watching with mounting concern.

Many in Mr Trump’s court—including J.D. Vance, the vice-president, Tulsi Gabbard, the director of national intelligence, and Pete Hegseth, the secretary of war—took part in previous ground wars in the Middle East. They all concluded that those conflicts had ended up as grand follies. They should speak up about the dangers now.