Just Because You're Paranoid...
So most of the reason that Iran's president (and the clerics who actually run the country) are so insistent on defying the world and developing nukes is that they're paranoid and smugly convinced of their own righteousness. They tend to talk about America as the imperialist Great Satan for the same reason.
Even so, I can still sort of understand their concern. The Pres. & VP still intermittently saber-rattle about Iran, which can't help, but the current physical, military realities can't have escaped the Iranian leadership's attention. Specifically, the two countries that share Iran's most important borders--Iraq and Afghanistan--are under US-led occupation. Nearby Saudi Arabia is home to US military bases, and bordering Pakistan gets a lot of military support from the US. We have them surrounded.
Under those circumstances, I'd be pretty skeptical of America's intentions also. But then I know that we're not a bunch of gun-happy idiots bent on a disastrous occupation of a nation WAY BETTER equipped to fight our army and then, even if it were to lose, positioned to conduct a generations-long insurgency.
We're not, right?