Would Tehran Do the Unthinkable?

Would Iran use a nuclear weapon?

This is something of a hobbyhorse, I admit, but I find it striking that people who would presumably know better casually float the idea that the Iranian leadership would launch a nuclear weapon at Israel or the United States:

As I've noted before, Iran has had WMD for roughly two decades and they have not used it against Israel or the United States. Nor have they transferred those weapons to Hamas and Hezbollah for a more covert attack. Of course, it's possible that some faction of the Revolutionary Guard might decide that watching Tehran be leveled in a nuclear blast is a bright idea, but it's not especially plausible. And plausibility, not possibility, is what we're ultimately talking about.