Carson is a low energy loser
Why is he surging in the polls then?
It's mostly evangelicals being the first GOP group to find a candidate to begin to coalesce around in Carson. But while an evangelical candidate can win Iowa, they will get their ass kicked in NH, and are very unlikely to win in SC. Carson's style appeals to this types of voters while most voters will be skeptical about him.
In my mind this is actually not too bad for Trump. If Carson keeps the Evangelicals out of a more viable candidate's hands than that's good for him.
Carson is surging in New Hampshire as well. In South Carolina too. Everywhere, really.