According to Rasmuusen Reports:
The addition of former Tennessee Senator Fred Thompson (R) to the list of candidates shakes up the race for the GOP Presidential nomination.
Former New York City Mayor Rudy Giuliani (R) remains on top, but his support dips below the 30% mark for the first time in seven weeks. With Thompson in the mix, Giuliani's support tumbles to 26%, down nine points from a week ago. That's the lowest level of support measured for Giuliani in any Rasmussen Reports poll this year.
Support for Arizona Senator John McCain remains steady at 16%, but McCain's hold on second place is threatened by Thompson. The movie star turned Senator turned TV star weighs in with 14% support among those likely to vote in a GOP primary. Among Very Conservative voters, Giuliani attracts 20% support followed closely by Thompson at 19%, former House Speaker Newt Gingrich at 18% and McCain at 14%.