Rudy Giuliani has fallen from first to fifth while Mike Huckabee holds a double-digit lead over second place Mitt Romney in a new SurveyUSA poll of 593 likely Republican voters.  John McCain continues his rise — only two points behind Romney in third — and Fred Thompson is only a point behind in fourth.

The poll was conducted from Dec. 17-18.

1. Mike Huckabee 28%
2. Mitt Romney 18%
3. John McCain 16%
4. Fred Thompson 15%
5. Rudy Giuliani 12%

(h/t Race42008)