DES MOINES – The Democrats in Iowa are having a caucus on Tuesday night, but of course President Obama is unopposed. In the hotly-contested GOP race, former Massachusetts governor Mitt Romney is the favorite, but former senator Rick Santorum and Rep. Ron Paul are close in most polls.

Here’s a look at the various scenarios on the GOP side, and how they could have affect Obama’s chances of winning in November.

1. Romney wins easily

A victory by the former Massachusetts governor of five points or more would make it very difficult for his rivals. Romney would almost certain win the Jan. 10 primary in New Hampshire and would be a favorite even in South Carolina.

Romney wrapping up the nomination is not ideal for Obama. A longer primary would force Romney to adopt more of the rhetoric and positions of the Tea Party, making it harder for him to win the general election. A quick victory by Romney allows him to focus intensely on the independent voters who usually determine the election winner.

2. Romney wins, but by a very close margin

A narrow Romney victory would still make him the heavy favorite to win the nomination. But it would further illustrate his weakness with Tea Party voters in the GOP and embolden the other candidates to aggressively compete with him in South Carolina and Florida. A longer GOP primary is ideal for Obama.

3. Ron Paul wins

The libertarian has a strong core of supporters who will support him no matter what, but they are a fraction of Republican voters and he will almost certainly not win the nomination. Many Tea Party conservatives are as wary of Paul as they are Romney.

A win by Paul would be another illustration of the slim support Romney has in the party. And it would elevate the public attention on man in Paul, who has some very controversial views that could shed a negative light on the GOP. All of this could help Obama in the short-term.

But ultimately, a Paul win means one of the candidates who could potentially organize most conservatives (like Rick Santorum or Rick Perry) has not won Iowa. So it would lead to a Romney nomination.

4. Former Pa. Sen. Rick Santorum wins

This would be one of the best outcomes for Obama. Santorum would immediately be a threat to win South Carolina and other states by consolidating the conservative vote.

Obama aides for months have been trying to get one of the conservatives to take on Romney aggressively, and Santorum would no doubt do that. At the same time, Santorum was easily defeated in his 2006 reelection campaign in Pennsylvania and would be a weaker general election for Obama than Romney.

5. Perry, Gingrich or Bachmann wins

This is highly unlikely, but would be the best outcome for Obama. Perry and Gingrich have the funding and bases of support to win the nomination. They would give Romney a real fight and along the way push him to the right, a development that could aid Obama in the general election.

And Perry and Gingrich have obvious flaws, particularly Perry’s debating skills, that would help Obama in the general election if either was nominated.