Boy, that sounds like the definition of second tier. Most common second choice=least common first choice. If Thompson doesn't come in 3rd in Iowa, he's done. He's got no chance in NH or Michegan. Last I checked he wasn't even winning in SC, which is supposed to be his turf. Favorability? How about straight up leading in a poll? How bout a number not in the teens in any state?
Boy, that sounds like the definition of second tier.
With 50% of the voters expressing either "unknown" or enough uncertainty about their 1st choice to change their minds, it means a lot more than that.
Don't forget the Iowa is a caucus state, which basically allows folks to convince each other as the votes are happening -- with the support for all candidates across the board being as soft as it currently is, almost nothing should be considered unlikely as a result.