Iran understands that they can’t produce enough bombs to destroy the West. But they might hope that a bomb smuggled into Russia and detonated at the right place and time might trigger a Russian nuclear attack on the West. The Russians aren’t known for their sophistication.
The hell they don't. It only takes one.
They aren't stupid. They have been practicing launching Shahab 3s from container ships. Explode one of those things high enough in the atmosphere over the CONUS and it's "hello, 19th century."