The uncertainty tells us something important about these early polling states. Old fashioned politicking and candidate shopping will be rendered irrelevant by diversity. In diverse states and nations, you don't vote for ideas, you vote for the leader of your tribe. Already, you can see signs of this in the Democratic primaries, where Hillary Clinton is the candidate of the minority vote and Bernie Sanders the candidate of "Bernie Bros" and affluent white urban liberals.
But New Hampshire, like Iowa, is still mostly white. So voters in New Hampshire are still "candidate shopping," going from one rally to the next and trying to make up their mind. This is why Marco Rubio's flub in the recent debate was such a disaster; New Hampshire voters really care about these kinds of things.
Voters who would have gone with Rubio are giving a second look to candidates such as Jeb Bush, John Kasich, and also rans like Fiorina and Christie. The media Narrative also seems to have shifted. Instead of "Marcomentum," we now have Jebmentum, especially as Jeb is trying to define himself as the one candidate willing to take on Donald Trump.
New Hampshire is known for last minute swings. In 2008, Barack Obama was leading every single poll going into the vote by as much as nine points. Hillary Clinton ended up coming out on top by 3, delaying Obama's coronation and leading to hard fought contests in other states. Trump, despite his lead, could suffer the same fate.
However, Trump has one critical structural advantage. Unlike Hillary in 2008, Trump is not facing one other candidate, he's facing several. Cruz has locked down most of the "very conservative" vote and is chasing the libertarians, but there simply aren't enough of them in New Hampshire to give him a victory. Cruz may well place in second because of his superior organization (the best of any of the candidates nationwide) but a victory would be almost unfathomable. A more likely challenger to defeat Trump in New Hampshire would be an "Establishment" Republican who can consolidate the anti-Trump vote. But they are all so busy attacking each other, none of them can do it in this one state.
It actually seems more likely Hillary could pull off an upset than any of the Republicans. After all, she's just competing against one guy.
What's more, the deliberative New Hampshire process ensures no one of these candidates is going to inherit all the undecideds. Assume NONE of the undecideds break for Trump. Even then, one voter might decide he likes Bush because he took on Trump, another thinks Rubio is the most electable, another may say Kasich has the best fiscal plan. Like a shotgun fired from a distance, the anti-Trump vote will be petered out. It looked as if Rubio could have consolidated it, but thanks to Chris Christie, it's hard to see him doing it over the next day.
Trump can take nothing for granted of course. And it remains to be seen whether his backers will turn out or if the Cruz machine will be able to "turn" some of his voters as they did in Iowa. But for now, Trump should feel optimistic.
The emerging Narrative is that Trump is petering out. But this is misleading. Every national poll still has Donald Trump as the national frontrunner. Ted Cruz's victory in Iowa has not led to a significant national bounce and the controversy over the Ben Carson vote means at least some people don't think Cruz even "really" won Iowa. If Cruz doesn't get second in New Hampshire, he'll be in danger of being thought of as a fringe candidate. There are no signs Bush or Rubio will drop out before South Carolina, no matter what happens. If Kasich gets 2nd in New Hampshire (which many polls think he will), he'll stay in longer as well, which works to Trump's advantage.
What does Trump want tomorrow? He needs a victory (obviously), giving him momentum going into Nevada and South Carolina. At this point, it's a must win because if Trump's huge advantage in the polls dissipates, the case would be made Trump voters actually don't exist. Unless every pollster in the country is completely incompetent, that seems unlikely (even other candidates' internal polls have Trump up by large margins.)
I'd argue he also wants Kasich in 2nd, ensuring Kasich doesn't drop out. He wants Bush in 3rd and Cruz in 4th (or even 5th). It would push Cruz to the sidelines, it would keep the Establishment divided, it would humble Rubio, and it would show the country Trump is unique because he can compete for the win in every single state.
If you're a Cruz supporter, you want second to support the idea that Ted really can win the nomination and compete everywhere. And given Cruz's organization, he shouldn't be discounted.
However, this is Trump's moment. If he can win a decisive victory in New Hampshire by double digits and if Rubio or Cruz doesn't come in second, Trump is going to look unstoppable going into the next few states. And after New Hampshire, there will be fewer undecideds and more diversity. Advantage: Trump.