Rasmussen reports that in the Iowa caucus, Mitt Romney leads former Speaker Newt Gingrich 23 percent to 20 percent, with Ron Paul close by at 18 percent. It’s a small margin, but it’s another sign that Gingrich’s support might be flagging in Iowa.

Gingrich may be relying on tonight’s debate in Sioux City to reverse his momentum. But Iowa political observers aren’t sure whether it will make up for his lack of campaign infrastructure:

Gingrich’s strong performances in Republican debates help his rise in the polls, said Iowa state Rep. Ralph Watts, but he hasn’t built an organization here. “I don’t think it’s much,” Watts said of the Gingrich campaign in Iowa. Watts, who is supporting former Massachusetts Governor Mitt Romney, said he had a tough time deciding between Gingrich and Romney.…

Organization matters more than the debate, because so many voters are undecided, Dallas County Republican Chairman Michael Elam said. “I think people are debated out at this point,” he said. “They are looking for someone who is going to be able to stand up above the fray.”

If Gingrich delivers another great performance and Romney wounds himself like he did during the last debate, it could certainly have an influence on undecided voters in the state. But it could all be a waste if Gingrich doesn’t back it up with daily on-the-ground campaigning – and oddly, Gingrich is spending little time in Iowa during the next three weeks:

After Thursday night’s debate, Gingrich will take a 2 ½ day swing through Iowa next week but will not return to the state until Dec. 27, when he plans to spend the final week before the caucuses on a statewide bus tour.

Gingrich’s decision not to spend more time in the Hawkeye State over the next two weeks is all the more risky considering his lack of an established turnout operation there.

Iowa is hugely important for Gingrich. As the frontrunner for the last few weeks, you’d think he’d try to wrap up the state by investing all of his time and energy there until the caucuses. Either he thinks it’s too late for retail politicking to make a difference, or he thinks it’s already in the bag and he doesn’t need to bother.