The GOP: Any poll aggregator will say that the national primary results are not good predictors of anything in most elections, but it is interesting to watch the rise and fall of candidates. If we just paid attention to this, it would say Trump is unstoppable, but as we know, the story looks to be different in Iowa at least. The other thing I find interesting about the national polls is that The Completely Sane and Honest Ben Carson hasn't sunk completely into oblivion. As in Iowa, he's still the fourth choice and no one else has risen above the None of the Above threshold, though Jeb:( is solidly in fifth with around 5%.
Iowa is less than two weeks away, and I expect nothing dramatic in the national polls until then, barring some major scandal.
The Dems: Looking at the national polls, you would think Hillary hasn't a worry in the world. Her numbers are still above 50%, Bernie can't crack 40%, it's all beer and skittles. But in the two states where people have to make their decision soon, she's got serious competition, where the most likely result right now is she will win Iowa and Sanders will win New Hampshire. Again, I think the thing most likely to move the needle nationally is the Iowa result in early February.