Updated

With the Iowa caucuses just 26 days away, the Republican presidential contest is now a two-man race. According to this week's Gallup poll, the two candidates with the broadest appeal to GOP voters are former House Speaker Newt Gingrich and former Massachusetts Gov. Mitt Romney. Asked who would "be an acceptable nominee for president," 62% said Mr. Gingrich and 54% named Mr. Romney. The only way anyone else becomes a serious contender is through a surprising finish in the Iowa caucuses or New Hampshire primary.

Mr. Gingrich has become the fourth front-runner in this year's contest, displacing businessman Herman Cain and now leading Mr. Romney in the RealClearPolitics average of recent polls, 31% to 20%.

Mr. Gingrich rose as Mr. Cain declined because of charges of sexual harassment and infidelity. He benefited largely on the strength of his debate performances. In the Nov. 30 Des Moines Register poll, 50% of Iowa Republicans said Mr. Gingrich was the best debater. Mr. Romney was a distant second with 14%.

While the race remains fluid (two-thirds of Iowa Republicans told CBS pollsters they could still change their minds), the former House Speaker has the advantage of the calendar. There are roughly two weeks until voters lay aside the campaign to focus on Christmas. Absent something extraordinary, after Dec. 21 the campaign will be influenced less by news stories, ads or debates and more by conversations around the dinner table and at holiday parties.

In the short run, Mr. Gingrich must temper runaway expectations. For example, his lead in the RealClearPolitics average in Iowa is 12 points. But what happens on Jan. 3 if he doesn't win Iowa, or comes in first with a smaller margin than people expect?

That could happen in part because Mr. Gingrich has little or no campaign organization in Iowa and most other states. He didn't file a complete slate of New Hampshire delegates and alternates. He is the only candidate who didn't qualify for the Missouri primary, and on Wednesday he failed to present enough signatures to get on the ballot in Ohio. Redistricting squabbles may lead the legislature to move the primary to a later date and re-open filing, but it's still embarrassing to be so poorly organized.

Organization truly matters, especially in low-turnout caucuses. Four years ago, for example, 118,917 Republicans turned out in Iowa—and only 424 votes separated the third- and fourth-place finishers. The total turnout was considerably less than the 229,732 Iowans who voted in the GOP primary for governor two years later. Being organized in all 99 Iowa counties means more people can be dragged to caucus meetings who might otherwise stay home on a wintery eve, believing their vote doesn't matter.

Karl Rove is a former senior adviser and deputy chief of staff to President George W. Bush. He is a Fox News contributor and author of "Courage and Consequence" (Threshold Editions, 2010). To continue reading his column in The Wall Street Journal, click here.