COL Gene, there are solid military, political, and practical reasons for dealing with Iraq first, and other rogue states afterwards. For example: We'd been in a state of war with Iraq since about 1991. The UNSC had repeatedly found the Hussein regime to be in violation of UNSC resoutions. Iran is difficult to pressure, without strong bases in the region; access to Iraq ends up being a strategic prerequisite to pressuring other state sponsors of terrorism in the region. As it turns out, if your long-term goal is to shatter the entire rogue states/state sponsors of terorrism paradigm, Iraq is a pretty good place to start.
The Iranian mullah's nuclear program was a lot further along than Saddam Hussein's, but the mullahs have been much more careful about not giving the civilized world plausible excuses to kick their ass. So they ended up a little further down the list than Saddam did. Now it looks like we're shooting for a self-determined regime change (and change of national heart) in Iran, in respone to recent world events.
Kim Jong Il is a totally different problem. We can't use force against North Korea, because North Korea can guarantee the immediate destruction of Seoul (using conventional or chem/bio weapons) no matter how the conflict ultimately ends. So that's why we didn't invade North Korea, but adopted a diplomatic approach instead.
Meanwhile... what motivates a shoplifter to run for the door faster? The clerk he knows doesn't care and won't bust him, or the loss prevention dude heading down the aisle straight towards him? Oh, no! By doing his job, the loss prevention dude has totally accelerated the shoplifter's getaway attempt! Clearly, we should just leave shoplifters alone! Besides, if both North Korea and the U.S. accelerate their programs (North Korea to have a nuclear deterrent, and the U.S. to stop them), then the relative rate of acceleration in the NK program is pretty much zero.
Seriously: If a gunslinger has been inching his hand towards his revolver all evening long, sooner or later his hand is going to be on the pistol grip. Then he'll draw, and then he'll shoot you. Sooner or later, his hand is going to be so close to his gun that you must draw, even if that means risking him out-drawing you. Your only other option is to keep waiting, which only guarantees that he'll out-draw you.
BARTENDER BILL: Hey, my shift is done, I'm outta here. You ready to take over?
BARTENDER GEORGE: Yep, sure am. You have a good night, Jake.
BILL: I surely will, Earl. Thanks! Oh, by the way, watch out for Black Bart, down at the end of the bar. He's been drinking heavily, and he's been edging his hand towards his gun. I reckon he's about ready to draw it now, and start shooting people.
GEORGE: The hell? And you didn't do anything about it?
BILL: Enh. I didn't want the hassle. You know how Bart gets. I figured I'd let you deal with it. Good luck!
