You can't tell countries not to get nukes or you'll nuke 'em!
You want non-proliferation, you make it clear that you will never use nukes.
But we all know why he won't rule out the nuke option with Iran. He's overextended our millitary on his bad idea called invading Iraq which has been executed poorly even in the opinion of those who supported the invasion to begin with. So, the nuke is the only realistic threat he has left. I hope we make it until we can get rid of this guy.