Last poll where we had that info is over a week old and things are moving fast
Since last month, however, Clinton was able to solidify her standing among some likely caucus–goers by increasing the number of people who said she would be their second choice. This is a critical factor in the Democratic caucus in Iowa. In the caucuses, a first round of “balloting” is conducted, and those candidates who do not win at least 15% support are ruled “unviable” and supporters are directed to a second choice among those who remained “viable” before a second round of “balloting” is conducted.
Last month, Obama and Edwards were much more preferred as a second choice among those candidates who appear to be unviable under Democratic caucus rules. Clinton appears to be gaining ground among those who might consider experience to be an important factor in choosing a nominee – she wins the lion’s share of support among those who make Biden their first choice, and she does well among those who would first choose New Mexico Gov. Bill Richardson.
Among those who make Obama their first choice, Edwards is their second choice, and vice versa. Among those who make Clinton their first choice, Obama is the favorite second choice.
http://www.zogby.com/news/ReadNews.dbm?ID=1395