What if the Republican nomination...

...comes down to a three-way race, between Marco Rubio, Donald Trump and Ben Carson?

Conventional wisdom has been that the GOP race would be between a "movement" conservative and an establishment candidate. Fair enough. And for much of this year Jeb Bush was thought to be that establishment choice; now it's Rubio. But it's safe to say it will be somebody -- maybe John Kasich, Chris Christie or even Jeb again.

What about the "movement" candidate? Many experts say Ted Cruz will ultimately occupy that space, and it's easy to see why -- he's raising gobs of money and running a smart campaign so far.

But Trump and Carson continue not to fade. In fact, if anything, Carson seems to be getting stronger. By many measures he is the front-runner: raising a ton of money, from lots of small donors, leading in many polls, etc.

And Trump, though slipping a bit, is still strong in many polls with less than a hundred days before the Iowa Caucuses.

Here's why I think it may turn into a three-man race. I don't have the polling data in front of me, but I've heard (or read) that not only do Trump and Carson draw from different populations, but their followers are also fairly committed.

Trump, I believe, attracts high school graduates who are mostly concerned with immigration. Carson, on the other hand, gets most of his support from college graduates who are also evangelical Christians. Apparently, there's not as much overlap as you might think.

So what if you get a three-way race between the establishment favorite, Rubio, and two "vanity" candidates, Trump and Carson, with the latter filling the "movement" space as well? Now, without getting into the weeds of how all the delegates are awarded, what if no one arrives at the convention with a majority? Could we really have a messy, brokered convention?