The problem is, Iran has been getting away with this behavior for decades. They know the Un is full of wimps, that it has no power over them. Plus, they have France and Germany in their back pocket, they have been doing shady deals with them despite any sanctions, so this makes the Un all the more toothless. In another corner, they have Putin(e) romancing them, and no doubt helping them along the nuclear path, all for a price mind you, such as pipeline easements, an oil field or two, no terrorist attacks (No Islamic expansion in Russian territory), and simular back door deals with China.
Carter showed them how weak America was in the 70's, and today the Democrats are showing them nothing has changed in that regard.
They know full well who they are "messing with" -unfortunately. They know Bush can stack the entire US fleet off their shore, but he can't use it.
What they don’t know is what a hated man in America will do with nothing, absolutely nothing to loose.