No. of Recommendations: 3
Why (does he have to know)? Why would you think that. In his mind, he could think it makes him tough.
Because he doesn't even threaten it. He never says, "If Iran doesn't behave, I'll nuke them." This is a man who will say anything, threaten anything, "float" any and every terrible idea he has. But he's never once mentioned using nukes.
He knows that's a line. He doesn't want to be Herbert Hoover, and he doesn't want to start WWIII. His base wants him to be tough, but he has at least some understanding on some level what nuclear weapons mean, and that it's a step you can't take without massive fallout (pun intended).