"Last night, I was talking with a pollster who kept insisting that Ahmadinejad was a nearly unique threat, as not only did he possess the means to eventually construct nuclear weapons, but he had a rationale for using them. I disagree on the last clause, but there is absolutely no reason to think President Ahmadinejad has the power to launch a nuclear strike. On anyone.
"In the Iranian political system, the Supreme Leader controls the armed forces, the television, the judiciary, the prisons, and basically every other lever of power. The President, conversely, is a very high-ranking civil servant. His only intersection with the military comes in the appointment of defense and intelligence ministers, who must then be approved by the Supreme Leader and then by the legislature. He is impotent when it comes to the armed forces...
"So President Khatami, who just wanted to institute some political reforms, was completely stymied by the Supreme Council. And yet we think Ahmadinejad will be allowed to launch nuclear attacks -- which will result in massive reprisal against Tehran -- all on his lonesome? It's nuts! He doesn't have the power. And no one with the power has proven particularly reckless or hungry for annihilating confrontation."
Ahmadinejad serves mainly as the comic book villain used to drum up popular American support for confrontation with Iran. I've noticed that here in Israel, where an Iranian nuclear bomb would represent a significant shift in its foreign threat level, there seems to be a lot more focus on "Iran" as such regardless of who's in charge. For the United States, however, the issue is concern over a possible competitor for dominance in a distant, yet strategically important region, and the propaganda factory needs a bit more "oomph" to keep people concerned.