After several months of only narrow or moderate leads over Democratic Senator Barack Obama, former New York Mayor Rudy Giuliani has surged to a 12-point lead over the man from Illinois. The latest Rasmussen Reports national telephone poss finds Giuliani with 51% of the vote to 39% for Obama.

That’s the biggest lead for Giuliani over the charismatic Democrat since December. Last month, Giuliani’s advantage was down to a single percentage point, 45% to 44%.

The new survey also shows Senator Obama continuing to lead former Republican Senator Fred Thompson. It's now Obama 47%, Thompson 44%. However, Thompson has gained a lot of ground in recent months. In May, Obama led Thompson by seven points. In March, his lead was 12 points.

Giuliani has been the Republican frontrunner throughout Election 2008. Thompson recently took the first formal steps towards an official campaign and moved into second place in the race for the GOP nomination.

Obama has consistently polled in second place among those seeking the Democratic nomination.

Obama is now viewed favorably by 50% of Americans and unfavorably by 44%. Those are the weakest numbers recorded for the Senator this year. His positive ratings have not been that low since January. Prior to this survey, the number with an unfavorable opinion of Obama has never topped 37%.

Opinion concerning Obama has changed little among Democrats. However, he has lost ground significantly among Republicans and unaffiliated voters over the past month.

Thompson’s numbers are currently heading in the opposite direction as he enjoys the status of being the new kid in town. Forty-five percent (45%) have a favorable opinion of him while 28% hold an unfavorable view. A month ago, 39% had a favorable opinion of him.

Giuliani continues to be the most popular candidate in either party. Currently 63% have a favorable opinion of him while 32% have an unfavorable view. His biggest challenge in getting the GOP nomination may be that only 21% of Republicans see him as politically conservative.

In the match-up with Giuliani, Obama's advantage with female voters gives him only a 46% to 45% edge among women. Meanwhile, Giuliani racks up a thirty-point advantage among male voters.

Thompson trails Obama by three points among unaffiliated voters, while Giuliani leads Obama by 15 points among that group. Rasmussen Reports surveys have shown the number of unaffiliated voters growing in recent months.

Mayor Giuliani also got a good report card, especially by Republicans, for his performance in the third debate, which aired June 5. Giuliani drew laughs after lightning disrupted his microphone as he was answering a question on abortion.

Rasmussen Reports continuously updates favorability ratings and general election match-ups for all Democratic and Republican candidates. Also available are continuously updated ratings for Members of Congress, Other Political Figures, and Journalists.

A recent tracking survey found that voters trust Democrats more than Republicans on ten key issues including taxes and national security. Democrats continue to lead on the Generic Congressional Ballot but their lead is smaller than a month ago.

Rasmussen Reports releases updated polling data for the Democrats’ nominating contest are updated on Mondays. Republican results are updated every each Tuesday

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