Iranian forces launched a big military exercise in the Persian Gulf Thursday, thereby underscoring a grim reality: The strategy for stopping Iran's nuclear program is turning into a race against time before options turn from mediocre to bad to worse.

The goal of American policy right now is to slow down the clock—that is, to stretch out the time Iran needs to become nuclear-arms capable. The hope is to buy time to give other kinds of pressure a better chance to work before military options move to the fore.

That's...