India, March 29 -- The news that Yemen's Iran-backed Houthis have entered the war, now in its second month, illustrates without any doubt that Donald Trump has backed himself into a corner over Iran. And it's a corner of his own making; strategic overreach paired with a fundamental misreading of leverage. What began as an attempt to coerce Tehran into submission has instead exposed the limits of American power in a conflict where the balance of incentives favours the other side.

When Trump's sweeping set of 15 demands first surfaced, even seasoned observers struggled to take them seriously. As one critic put it bluntly: "There's no way the Iranians would ever accept these demands." That scepticism has proved to be well founded. The probl...