Mitt Romney has extended his lead in the Iowa Republican Presidential Caucus for 2008 and three candidates are virtually tied for second place.

The latest Rasmussen Reports telephone survey of the race shows Romney with support from 29% of Likely Caucus Participants. Trailing the frontrunner by thirteen percentage points is Mike Huckabee who enjoys support from 16%. In a virtual tie for second with Huckabee are Rudy Giuliani at 15% and Fred Thompson at 14%. Further back are John McCain (6%), Ron Paul (4%), Tom Tancredo (4%), and Duncan Hunter (2%). Nine percent (9%) are undecided (see crosstabs).

Romney’s thirteen point advantage is double his six-point lead from a month ago. Support for Romney has increased four-points since the prior survey while Thompson’s support has fallen four points. Mike Huckabee is down two from the earlier survey suggesting his bounce may have reached at least a temporary plateau. Rudy Giuliani, the leader in national polls, picked up three percentage points over the past month.

Romney also enjoys a strong lead in New Hampshire, site of the first-in-the-nation Presidential Primary.

There are many challenges to polling a caucus, primarily around the question of who will actually participate. Those challenges are magnified this year by the timing of the caucus on January 3 forcing candidates and their teams to explore tactful methods of contacting voters during the holiday season. When only voters who are “certain” they will participate in the caucus are included in the totals, the race is a bit closer and Huckabee has a slightly more secure claim to second place. Using that tighter screening, it’s Romney 26% Huckabee 18%, Giuliani 15%, and Thompson 14%. (see discussion of methodology).

The race in Iowa is very fluid. Of the leading candidates, Huckabee has the most solid base of support but only 49% of his supporters are certain they will support him on January 3. Forty-one percent (41%) of Romney’s supporters are that certain along with 32% of Giuliani’s and 30% of Thompson’s.

Among those likely to take part in the Iowa Republican caucuses, Romney is viewed favorably by 76%, Huckabee by 65%, Giuliani by 74%, and Thompson by 73%. Those numbers reflect a six-point gain for Giuliani while impressions of the other candidates is essentially unchanged from a month ago.

McCain’s numbers, while still weak, have improved over the past month. Among Republicans likely to participate in the caucus, 61% have a favorable opinion of the Arizona Senator while 38% have an unfavorable view. A month ago, just 53% offered a positive assessment of the man once presumed to be the GOP frontrunner.

Ron Paul is viewed favorably by 33% and unfavorably by 55%.

Eighty-six percent (86%) of Likely Republican Caucus Participants say that when police officers pull someone over for a traffic violation, they should routinely check to see if that person is in the country legally. Eight percent (8%) disagree while 6% are not sure.

Seventy-six percent (76%) believe that if an illegal immigrant is discovered in this manner, they should be deported. Only 7% disagree.

Seventeen percent (17%) believe that this approach might create a temptation for police officers to discriminate while 73% disagree. On all of these questions, Iowa Democrats are somewhat more divided.

Only 5% of Likely Republican Caucus Participants believe undocumented workers should be allowed to get drivers licenses. Ninety-one percent (91%) disagree. Nationwide, 77% of all voters oppose drivers licenses for undocumented workers. Public opposition recently forced New York Governor Elliot Spitzer to drop his proposal for making licenses available to undocumented immigrants. (see video)

All polling for caucus events presents challenges in determining who is likely to show up and participate. In conducting and analyzing this survey, Rasmussen Reports reviewed results for many possible levels of turnout. While the results varied modestly depending upon the turnout model, the overall dynamic was the same in all cases—Romney in the lead with Huckabee, Giuliani, and Thompson close to each other in second. For example, our overall sample shows Romney with 29% of the vote and a thirteen point lead. When only those who were absolutely certain they would vote, Romney attracts 26% support and leads by eight. See information on screening questions and the sample used in this telephone survey.

Crosstabs available for Premium Members only.