Entering the month of August, it is quite easy to come up with an explanation for why each of the leading Republican Presidential candidates will not win their Party’s nomination.

Former New York City Mayor Rudy Giuliani is personally popular and has a solid core of support. But, it is easy to argue that America’s Mayor can’t win the nomination because his views on social and cultural issues step with a more conservative political party (just 27% of Republican voters see Giuliani as politically conservative while 68% say moderate or liberal). In this view, there is a ceiling to Giuliani’s potential support and he will not be embraced by a majority of Republican Primary Voters.

Former Tennessee Senator Fred Thompson is looking good as a non-candidate and has soared in early polling. But it is easy to envision Thompson tanking once he formally enters the race and is forced to endure the grind of debates and other routine challenges. Some Washington insiders expect Fred to fizzle and whisper questions about a lack of substance or fire in his belly. As with all such whispering campaigns, it is hard to separate legitimate expectations from the hopes of some insiders.

Former Massachusetts Governor Mitt Romney looks good on camera, on his resume, and in his bank account. But, he has failed to gain traction with GOP voters nationally. Even his advantage in New Hampshire polling is disconcertingly small for those who dream of Mitt in the White House. After all, he has a home field advantage in that state and is the only candidate so far to spend money advertising on television in that state. If he can’t dominate the field under those circumstances, how will he gain enough support to win the nomination? Besides that, 31% of Republican Voters have an unfavorable opinion of him.

Finally, there’s Arizona Senator John McCain. Of the four candidates in double digits, it’s the easiest to show why he won’t win the nomination. Within his own party, McCain is viewed favorably 54% and unfavorably by 40%. It is difficult to comprehend how anyone could win their party nomination with such high unfavorables among the party faithful. His long history of provoking conservatives was highlighted by his politically disastrous performance during the Senate debate over immigration. If you consider the financial crunch being faced by his campaign, the massive staff defections of the past month, and the negative impact of spectacularly missed expectations, it’s easy to count McCain out.

But, while it is easy to explain why each of those men will not win the GOP nomination, one of them will. McCain is certainly the least likely. His only hope at this point lies in the fact that the other three may all lose ground in the coming months.

It’s also tough for Romney to win without some help. However, if Thompson falters, Romney might be in the right place to pick up the pieces for Republicans who want somebody other than Giuliani.

It’s easier to see a path to victory for Thompson or Giuliani. Thompson has to show he’s for real after entering the race while Giuliani has to demonstrate he can reach out to some GOP voters who don’t share his position on cultural issues. But, those are significant challenges for the frontrunners.

It’s worth noting that in polling for the week ending August 5, 38% of GOP Likely Primary Voters support the top two candidates thought most appealing for conservative (Thompson and Romney). At the same time, 36% support the candidates thought most appealing to moderates in the party (Giuliani and McCain). Eighteen percent (18%) remain undecided.

Those latest weekly numbers show Giuliani with 25%, Thompson 24%, Romney 14% and McCain at 11%. Mike Huckabee earns support from 3%, Sam Brownback from 2% and four other candidates split 2% of the vote. Those candidates, mentioned by name in the polling question, are Ron Paul, Duncan Hunter, Tom Tancredo, and Tommy Thompson (review history of weekly results).

To keep you current on the daily numbers, Rasmussen Reports releases updated data from our Presidential Tracking Poll by noon each day, Monday through Friday.

In addition to the daily tracking poll, Rasmussen Reports provides weekly results to provide a longer-term overview of the race. These updates are based upon nightly telephone surveys. Results are reported based upon interviews conducted on the seven days up to and including the night before posting. The seven day results typically include interviews with more than 1,000 Likely Republican Democratic Primary Voters. This includes both Republicans Democrats and those independents likely to vote in a Republicans Primary. In some state primaries, independent voters are allowed to participate in party primaries while in others they are excluded. The margin of sampling error for the weekly update is +/- 3 percentage points with a 95% level of confidence.

Updates prior to July 16 were based upon four days of polling conducted the Monday through Thursday preceding release.

Rasmussen Reports continuously updates general election match-ups and other measures for all Republican and Democratic Presidential candidates. Also regularly updated are favorability ratings for Members of Congress, Other Political Figures, and Journalists along with public attitudes towards Congress, the War on Terror, and other topics. Results for the Generic Congressional Ballot are updated monthly.