Does the term “all’s fair in love and war” sound familiar? 
Here’s the thing: officially, the United States does not condone, nor practice assassination. What they do unofficially is left to the imagination of conspiracy theorists. In wartime, however, it’s not considered assassination if you strike an important military complex with the idea of say, “disrupting command and control.” Thus if you hit a bunker containing suspected weapons munitions, or a command center, and Saddam happens to be in residence, well, it’s simply a “lucky coincidence.” What’s important is that you’re not singling out one specific individual as a target. It’s all in the wording.
Of course, this doesn’t explain snipers. Typically, snipers are after targets of opportunity rather than a specific individual. Their goal is to disrupt enemy command and undermine troop morale. If they just “happen” to be in an area frequented by an enemy leader, how…lucky. Again, it’s all in the wording.
Make no mistake, during wartime, both sides are trying very hard to locate the top commanders so that they can kill them. It’s part of war, and both sides are in on the fun. You want to talk about wording? War is murder on a massive scale. Because it’s called “war,” however, it’s okay to kill your fellow man. War gives us license to do, as a group, what we would not do as individuals.
Without running off to the search engines myself, does anyone recall when Saddam tried to assassinate President Bush? My guess is that it was after Desert Storm had ended. That takes it out of the wartime arena, with all of it’s rule bending, and places it firmly in the illegal catagory.
There might also be some distinction as to the method involved. Is a bomb dropped from a plane the same as a bomb strapped to the underside of the President’s car? I think so. My guess is that most Americans would consider it bad form if we had strapped a bomb to Saddam’s private car, even during the Persian Gulf War. America prides itself in being the good guy, and car bombs seem underhanded compared with a laser guided bomb.