It's a slim lead, and if things shake out the way the most of the polls are saying, Romney will eke out a narrow win with Paul and Santorum very close behind.

PPP:

The Republican caucus in Iowa is headed for a photo finish, with the three leading contenders all within two points of each other. Ron Paul is at 20%, Mitt Romney at 19%, and Rick Santorum at 18%. Rounding out the field are Newt Gingrich at 14%, Rick Perry at 10%, Michele Bachmann at 8%, Jon Huntsman at 4%, and Buddy Roemer at 2%.

The momentum in the race is completely on Santorum's side. He's moved up 8 points since a PPP poll earlier in the week, while no one else has seen more than a one point gain in their support. Among voters who say they decided who to vote for in the last seven days he leads Romney 29-17 with Paul and Gingrich both at 13.

Santorum's net favorability of 60/30 makes him easily the most popular candidate in the field. No one else's favorability exceeds 52%. He may also have more room to grow in the final 48 hours of the campaign than the other front runners: 14% of voters say he's their second choice to 11% for Romney and only 8% for Paul. Santorum's taken the lead with two key groups of Republican voters: with Tea Partiers he's at 23% to 18% for Gingrich, 16% for Paul, 15% for Bachmann, and only 12% for Romney. And with Evangelicals he's at 24% to 16% for Gingrich, and 15% for Paul and Romney.

Other than Santorum's rise the other big story of this week is Paul's fall. He was at 24% earlier in the week but has dropped to 20%. That decline in support coincides with a precipitous drop in his favorability numbers. On our last poll he was at +13 (53/40), but that's gone down 21 points on the margin to -8 (43/51).

Romney is also still comfortably ahead in New Hampshire. Will the one-two punch of Iowa and New Hampshire start the ball rolling for Romney when the race heads south to SC and FL? This is especially interesting given the recent surge of Santorum.The former Pennsylvania senator's national numbers haven't shown much movement - yet. If he were to totally surprise and win in Iowa, that will almost certainly change, making him the major alternative to Romney.

But if Romney were to catch fire in South Carolina (primary on 1/21) and win, it is difficult to see where he might be stopped. Florida (primary on 1/31) is Jeb Bush country, and while the former governor has yet to formally endorse any candidate, it is believed by some he is will quietly pass the word and throw his support behind Romney.

Still, 30 days is an eternity in politics - especially in this race. About the only guarantee is that there are still some surprises left before a nominee emerges.