Read full Newsweek/Princeton Survey Research Associates poll

Mike Huckabee now leads Mitt Romney by a two-to-one margin, 39 percent to 17 percent. The next three leading candidates, who all show signs of fading in Iowa: Rudy Giuliani, who dropped from 15 percent in the last survey to 9 percent in the current one; Fred Thompson, who fell from 16 percent to 10 percent; and John McCain, who slipped from 7 percent to 6 percent. Among likely GOP caucus-goers, 57 percent name Huckabee as their first or second choice and 39 percent give Romney as their first or second choice. On this measure, Thompson is a distant third, with just 20 percent. Huckabee’s religious credibility, by the same token, appears to be a key factor behind his surge.

Barack Obama has gained some ground, moving to within a point of Hillary Clinton among all Democratic voters (29 percent vs. 30 percent), with John Edwards in third place at 21 percent. Among those most likely to attend the caucuses, Obama has moved substantially ahead of Clinton, 35 percent to 29 percent, while Edwards falls back a bit, to 18 percent. While the Illinois senator’s lead among Democratic caucus-goers in this poll is not large enough to be statistically significant, Newsweek says things seem to be trending his way.