With Fred Thompson poised to formally enter the Republican field soon, the latest Gallup poll shows former Mayor Rudy Giuliani still leading the pack by double digits. He commands 32% support among likely GOP primary voters as Thompson draws 21%, McCain 16%, and Romney gains 9%. Thompson and McCain have essentially switched positions and numbers over the last six weeks or so.

Rudy's lead isn't nearly as formidable as Hillary's on the other side, though. Key factors to watch are reported by Joseph Carroll and Jeffrey M. Jones for Gallup:

Giuliani is the first or second choice for the nomination of 52% of Republicans -- well ahead of any other Republican on this measure -- as he has been all year. Thirty-one percent of Republicans rate Fred Thompson as their first or second choice, 30% name McCain, and 18% name Romney.

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Turnout may be more of a factor in the Republican primaries than the Democratic primaries. Among the 61% of Republicans in the last two polls who say they are extremely likely to vote in their state's primary or caucus next year, Giuliani (29%) and Fred Thompson (25%) essentially tie. McCain is third among this group at 18% and Romney fourth at 9%, with all other candidates at 3% or below.

The full details are at the link above (scroll down past the Democratic results). Retaining a majority on the "1st or 2nd choice" question makes Rudy the odds-on favorite to win, and most able to unite the party after the primaries. His slimmer lead among those almost certain to vote likely indicates that a significant portion of his support comes from Republican-leaning and non-aligned independents - voters who might have been expected to support McCain. UPDATE 6:22 p.m.: As noted by Cliff McKeithan in the comments, 52% is NOT a "majority" in this case - sorry!

The big question hanging over the GOP nomination remains, "How will Thompson do when he is 'really' running?" Fred has run a spectacularly brilliant "pre-campaign" so far, and all indications are he will enter instead of pulling a Mario Cuomo (who was the favorite of Democrats in the early stages of the 1988 and 1992 primary seasons, but never became a candidate). A lot depends upon McCain: much of his support would presumably tend to go to Thompson if the Arizonan drops out. The longer McCain hangs on, the more difficult it is for Fred to make headway.

Mitt Romney holds the other wild card. He has thrown "all in" to organize for Iowa and New Hampshire (he spent heavily in South Carolina early, but seems to have backed off a bit once Thompson's entry began to look inevitable). So despite his scant national standing, he could make a huge splash in January. Since the Iowa caucuses first garnered national attention in 1976, no candidate who won both Iowa and New Hampshire failed to win his party's nomination. In fact, though, no non-incumbent Republican hopeful has ever won both Iowa and NH.

At this stage, the GOP nomination process looks to be the more interesting of the two parties.