The summer months showed just how far ahead Hillary Clinton is in the Democratic presidential race. September will go a long way toward bringing some, but not nearly as much, clarity to the Republican nomination contest.

That's because we should know after a few weeks on the campaign trail whether former Sen. Fred Thompson, who formally began his campaign last week, is as good a candidate in the flesh as some think he is on paper.

If so, then he will quickly become a major force in the Republican race along with former New York Mayor Rudy Giuliani and former Massachusetts Gov. Mitt Romney.

And that would likely doom the candidacy of Arkansas Gov. Mike Huckabee, who had his moment at the Iowa straw poll, and will also make it clear that Newt Gingrich is as likely to enter the race as the pudgy former U.S. House speaker is to play in the National Basketball Association. Both developments would help Thompson a good deal.

Although many in the media continue to portray the race for the Democratic nomination as strongly competitive, the numbers paint a different picture. Other than in Iowa and New Hampshire where she is competitive, Sen. Clinton is far ahead — as much as 30 points in some major states — of the field.

But the Republican race, which has taken a back seat due to the media focus on the confrontation between Sens. Clinton and Barack Obama, has been in flux for some months.

When the race began last winter, Sen. John McCain of Arizona was the odds-on-favorite for the nomination and many thought that Giuliani's support for abortion rights, gay rights and gun control would make him persona non-grata with GOP primary voters.

McCain is now being written off by some, while Romney, still relatively unknown nationally, is considered by many to be Giuliani's major challenger. Giuliani leads in national and many state polls, but not by as much as does Sen. Clinton among the Democrats. Romney leads in Iowa and New Hampshire.

The reason for the current uncertainty is Thompson. His appeal is at least partly because of his celebrity status, but also because many GOP activists see him as the type of Sun Belt conservative who generally wins the nomination. That would make him the likely heir to the Huckabee and Gingrich voters, should they decide to go elsewhere. Even as an undeclared candidate, Thompson has risen to second in most GOP polls.

But he lacks the campaign structure that the others took months to build, and will find himself in the spotlight once he becomes an active candidate — which could propel or ruin his candidacy.

If his reviews are good, then he will likely shoot up in the polls. That's because Giuliani's lead is a tenuous one, and appears to be built as much on name recognition as legions of deeply committed followers.

The Gallup Poll's savvy Lydia Saad makes a strong argument based on the polling data that Giuliani's lead is built strongly on greater name recognition among Republican voters and is likely much less solid than Sen. Clinton's among Democrats.

"The implication is that Giuliani is at greater risk than Clinton in losing support as the campaign progresses and his opponents become better known," she wrote. "Giuliani's is quite strong among" the 54 percent of Republican votes who say they are not familiar with the broader field of candidates; "but among those (46 percent) who are familiar with all four" of the leading GOP candidates — Giuliani, McCain, Romney and Thompson — Rudy trails Thompson.

Hence the enormous opportunity that Thompson has to introduce himself to many voters as his campaign kicks off. Among those who know him, Thompson is viewed favorably by 10 times as many Republicans as unfavorably, the best ratio on that key metric of any candidate. If he can hold that margin as he becomes better known, then his support in horse-race match-ups is certain to rise.

However, if Thompson does not show well on the trail — and the key will be a mistake-free tour that convinces GOP voters he is both competent to be president and has an agenda to their liking — then Romney, and perhaps Huckabee, would benefit.

Regardless of how he does, Thompson's entry will bring some clarity to a muddled Republican contest.

Peter A. Brown is the assistant director of the Quinnipiac University Polling Institute. Reach him at peter.brown@quinnipiac.edu. This article first appeared on www.Politico.com.