@puzzledperson,
Here's a link to a University of New Hampshire poll, three days old, showing voter certainty levels both before and after the Iowa Caucus.
For Republicans who say they plan to vote in the New Hampshire primary (6.8% margin of error) polled after Iowa:
Definitely decided: 41%
Leaning toward someone: 25%
Still trying to decide: 34%
If vote were held today, would vote for:
Trump: 29%
Rubio: 18%
Wouldn't vote for under any circumstances:
Trump: 37%
Rubio: 5%
With 34% undecided and 25% only leaning toward a candidate, that leaves an awful lot of uncertainty among likely Republican primary voters in New Hampshire. So the fact that Trump leads by 11% over Rubio if the vote were held today, doesn't prove a lot, since that type of poll requires respondents to choose among candidates and does not allow "undecided" as a poll response. (It does allow "other" but that means other candidates, perhaps write-ins, or at least more obscure ones).
http://cola.unh.edu/sites/cola.unh.edu/files/research_publications/GOPPrimary_20416.pdf