Why Hillary and Not Clinton?

I know, like I don't have more important issues to ponder or tasks that need my attention. This has been rolling around in my head for a while now, so maybe if I write it down I can let it go. If I asked someone why, I'd probably get the answer that we call her Hillary to differentiate her from former President Bill Clinton. But that isn't totally plausible since we call our current president 'Bush' most of the time. Yes, he can be referred to as George W., but he's usually not.

So why aren't we referring to Hillary Clinton as just Clinton? I think there's something there.

I haven't decided who's getting my vote on Super Tuesday, so what I'm saying here has nothing to do with supporting or not supporting Clinton. I feel like referring to her on a first name basis when we're not referring to the other candidates as Barack, John E. and John M., Mitt, Mike, etc. says something. Like somehow she isn't on the same level as the other candidates, maybe not respected as much because, dare I say it, she's a woman. Maybe it's because her first name has a musical ring to it, and it rolls off the tongue more easily than 'Clinton'.

Whatever the reason, I will refer to her by her surname as I do all the other candidates.