Try this by way of hypothesis (with all the health warnings that these polls carry as given)
The Iowan God vote as represented by Cruz and Carson has been worth about 35-38% since about November. It's a bit lower at the moment at 33%
Lets assume that Carson does get a bounce. He's been as high as 29% when Cruz was still in single figures, so there might not be too much downside left. Let's crudely give him 12-13% and then accept (which is a bit of an ask admittedly) that there is a relationship with Cruz and he drops to 20-22% (work with 21%)
The next jump we make is that Trumps vote might not exist. Let's say 1 in 3 won't show, and reduce him from his current mark of about 31 to say 21%
So we have some silly hypothetical hierarchy of;
Cruz = 21%
Trump 21%
Carson = 13%
and 44% in play
As things stand, Rubio is accounting for about 45% of what's left but showing signs of a late upswing (I'll stop short of calling it a surge). This would give him a closing in 20%
Oh bloody hell, this could be really close yet.
OK, (I'm) relying on three things
1: Carson to get a bit of a late bounce (not without foundation, but I'm damned if I can see what he's done to deserve it)
2: Carson to get a swing from Cruz (this has been a pattern, but again I'm damned if I really understand it, and can't dismiss coincidence as an explanation)
3: Trumps vote to fail to turnout (anyone's guess)
Rubio could still be value at 12/1
I can certainly see him first two
