If Fred Thompson, former Senator from Tennessee and Law of Order actor, enters the Republican field, the conventional wisdom is that he would gain support from the social conservative bloc of his party. Just starting in their latest poll did the Washington Post and ABC News include Fred Thompson in the list of Republican candidates. Thompson captured 9% of the vote. Two people dropped significantly: Giuliani falling 11%, Gingrich dropping 9%, and McCain holding steady. In the same poll, excluding Fred Thompson from the field, Giuliani jumped the most out of any candidate, getting an additional 4%.
When Gallup first introduced Thompson into the Republican candidates in their March 23-25 poll, he garned 12%. In that time period, Giuliani dropped 13%, Gingrich fell 1%, and McCain had a slight uptick of 2%.
The polls seem to indicate that a Thompson entry would hurt Giuliani the most. This leads me to believe that social conservatives were supporting Giuliani before rumors of a Thompson bid affected the field. Even though Giuliani has previously expressed liberal views on social positions, the other two of the Big Three have changed their minds on the issues, especially Mitt Romney. With no strong candidate backing up their beliefs, the social conservatives go towards Giuliani and the image of his strong post-9/11 leadership.