The long-anticipated entry of former Senator Fred Thompson is now a fait accompli, so while his first debate performance and the third-quarter fundraising numbers remain to be seen, the field seems set - despite the Gingrich head feint. My analysis of the race as it stands before those results are in:

Giuliani appears to be retaining a slim lead, although his support has been steadily dwindling since early spring. The average of recent national polls at Real Clear Politics sees Rudy with 28.2% support, followed by Thompson's strong entry at 22.9%. McCain has moved back into third place with an average of 15.2%, his best showing in some time. Romney has slipped back nationally, losing the bump from his win at the Ames, Iowa Straw Poll, to 9.1%, while Huckabee trails at 4.1%, but seems to be riding a minor uptrend.

Giuliani's central appeal to Republican primary voters is electability. He seems most likely to attract swing voters and Democrats. His very positions on social issues that give him this crossover potential also diminish the enthusiasm of social conservatives, traditionally the GOP's top source of volunteers and activists. This may account for the slow erosion of his support, as other candidates emphasize their social conservative positions.

Surprisingly to some, some poll internals show McCain moving into second place when the question is broadened to "first or second choice." This may reflect the attention moving from the immigration bill, which hurt McCain with the GOP base, and Iraq, where he is strongest. Since Iraq appears likely to be the central issue of the 2008 campaign (all the Republican candidates favoring staying until goals are achieved and all the Democrats advocating swift withdrawal regardless of facts on the ground), this works to McCain's political advantage. He's still a long shot at this point in the campaign, but ruling him out is premature.

Romney has failed to capitalize on his momentum from Ames, and the attention paid to the entrance of Thompson, McCain's "owning the surge," and Giuliani's public conflict with MoveOn and the NYT has sucked the oxygen out of his campaign. He still holds a substantial lead in Iowa polls, and that state depends on organization, an area upon which Romney has spent much and well. His lead over Giuliani in New Hampshire has shrunk to about the MOE, though, imperiling his early state strategy. Michigan's move to the front of the primary schedule should help him, though: he is a native and his father was a very popular three-term Governor. Given his failure to gain a larger national share, the early contests become critical for his campaign.

Despite his gaudy numbers, Thompson remains a dark horse. His performances in the upcoming debates and in fundraising could establish him either as the man to beat or as an also-ran. His weakness is his strength: he wouldn't lose a southern or border state, but could he hold the battleground states in the midwest and west? What "blue state" could he turn?

Any honest evaluation must judge the Republican contest as wide open. Some candidates would certainly surprise by winning the nomination, but none of the top four would be a shock.