Over the next three weeks, the heat-to-light ratio in the press coverage of the Iowa caucuses will rise steadily. Here are a few basics to keep in mind.

1. Iowa is a flawed leading indicator, especially for Republicans. Of the past five contests without an incumbent Republican president, the Iowa winner has gone on to receive the nomination only twice—in 1996 (Dole) and 2000 (George W. Bush). On the other hand, Iowa typically winnows the field and seems likely to do so again. If Bachmann and Santorum don’t do significantly better than expected in Iowa, their campaigns for all practical purposes will end. If Perry doesn’t do well despite spending millions on advertising, he’ll probably have enough left in the bank to continue, but with poor prospects of success.

2. A Gingrich victory in Iowa would put him in a strong position to go the distance—by narrowing or even overcoming Mitt Romney’s margin in New Hampshire and by putting him in an excellent position to sweep the Southern primaries, where he now leads Romney by a combined 41 to 16 percent.

3. Ron Paul is Romney’s new best friend. Not only is Paul attacking Gingrich relentlessly, but also a strong Paul showing in Iowa would almost certainly come at Gingrich’s expense. Because Romney is unlikely to prevail in Iowa, the best outcome for him would be a victory by a candidate with no chance of going on to win the nomination. More than a few veteran observers of the Iowa scene believe that Paul’s combination of strong organization and fervent support could produce just such a result.

4. Paul is not the Tea Party candidate. In fact, 56 percent of likely Republican caucus-goers who sympathize with the Tea Party have ruled out voting for Paul—more than for any other candidate. By contrast, only 17 percent have ruled out Gingrich, while only 31 percent have done so for Romney. The reason is simple—Tea Partiers are fervent across-the-board conservatives, not libertarians, and disagree with Paul on many social and foreign policy issues. Indeed, Paul’s profile disrupts standard ideological categories. 13 percent of Republicans see him as liberal, 20 percent as moderate, another 20 percent as somewhat conservative, and 28 percent as very conservative, while the remainder just don’t know what to make of him.

5. Romney and Gingrich’s ideological profiles are much clearer to voters. Likely Republican primary and caucus participants have found it much easier to locate Romney and Gingrich along the left-right continuum. 57 percent see Gingrich as somewhat or very conservative, versus 28 percent who regard him as moderate. Romney profile is almost the mirror-image: 53 percent see him as moderate, versus only 29 percent as somewhat or very conservative. In a party whose grassroots supporters are mainly conservative, Gingrich’s ideological position gives him an advantage—if he can maintain it. That’s why Romney and others have begun attacking him for past positions that defied conservative orthodoxy.

6. Romney has lost his “electability” edge: What was once his greatest asset among Republicans—the belief that he was far more likely to defeat Barack Obama than was any other contender—now seems to be slipping away. As recently as mid-November, fully 30 percent of primary and caucus participants espoused that view, versus only 13 percent for Gingrich. Now, 35 percent give the electability award to Gingrich, versus 28 percent for Romney.

Are these Republicans right? Based on the evidence, anyway, it’s hard to say. On the one hand, a synthesis of recent surveys suggests that Obama would beat Gingrich handily but is in a dead heat with Romney. On the other hand, a recent Gallup/USA Today poll showed that both Romney and Gingrich lead Obama in the twelve crucial swing states by almost identical margins. And one could make a case that Gingrich’s more welcoming stance on immigration would serve him well with Hispanics in a general election—assuming that it doesn’t become his Achilles heel during the nominating contest.

7. The Republican race remains fluid and unsettled. Only a third of Romney’s supporters back him strongly; only 29 percent of Gingrich’s do so. And there are indications—from the Gallup tracking poll, for example—that the Gingrich tide is receding a bit. A poorer than expected showing in Iowa could disrupt the momentum of his entire campaign.

William Galston is a senior fellow at the Brookings Institution and a contributing editor at The New Republic.