The public perception of Kerry isn't his fault. It's this real simple guy thing. Kerry has been in a war, so he doesn't feel the need to act like an ass-kicker. So he doesn't come off as one.
Bush hasn't been in a war, so he has something to prove. He feels he has to act manlier to compensate for the fact that he never knows what the hell he's talking about. He doesn't really know what staying on the offense means in human and global cost, so he can say it and sound like he has conviction. He isn't burdened with the thought in the back of his head that "some poor guy is gonna die because of my lies" because he clearly kind of enjoys that part, just as he clearly has no experience beyond being a whiny rich boy. He's the short upper-middle-class kid who plots to blow up the school.
He looks like he kinda wants to take a swing at Kerry, too, which I hope he does in the next debate, because Kerry would hand him his free-world-leading ass in about two seconds.