With just three and a half weeks until the Iowa caucus, Donald Trump is still the front-runner for the Republican Presidential nomination. Or is he? Photograph by Spencer Platt / Getty

With just three and a half weeks to go until the Iowa caucus, Donald Trump’s bubble shows no signs of bursting. Earlier this week, more than eight thousand people turned up to see him in Lowell, Massachusetts, which is just across the border from New Hampshire. On Thursday night, a similar-sized crowd is expected to attend a Trump rally in ultra-liberal Burlington, Vermont—the home base of Bernie Sanders. And the first poll of the new year from New Hampshire, where voting will take place on Tuesday, February 9th, shows Trump retaining a big lead over the other G.O.P. candidates.

Among the commentariat and the political class, there are, broadly speaking, two views. The skeptical one is that, even at this stage, the crowds and polls don’t have much predictive value, and that Trump remains highly unlikely to win the nomination. The other view is that Trump’s campaign is still gaining ground, and that he has a very realistic chance of victory.

At this stage, I’m going to remain agnostic and confine myself to laying out some of the numbers and the arguments. However, as I pointed out before Christmas, Trump’s poll numbers can no longer be dismissed as a Michele Bachmann/Herman Cain-style surge, and the possibility of him winning the nomination has to be considered. If Trump comes in second in Iowa and wins in New Hampshire—and that’s the outcome the polls are currently indicating—he would be in a strong position going into the South Carolina primary, on February 20th, and then the Nevada caucus, on February 23rd, and Super Tuesday, on March 1, when about a dozen states, many of them in the South, will vote.

Clearly, Trump has a substantial base of support among Republicans and Republican-leaning independents. Two big questions are whether he can get his followers to turn out at the polls in sufficient numbers, and if and when the non-Trump forces inside the G.O.P. will unite behind a rival candidate. The polls suggest that if they were to do this, Trump could be beaten. In the survey I mentioned from New Hampshire, which the research firm Public Policy Polling carried out, he has the backing of twenty-nine per cent of likely primary voters. That’s enough to give him a fourteen-point lead over Marco Rubio, who sits in second. But between them Rubio and the other candidates in the so-called establishment lane—Chris Christie, Jeb Bush, and John Kasich—have forty-seven per cent of the vote, enough to defeat Trump handily.

As long as all, or most, of these candidates remain in the race, they divide the moderate-conservative vote, and Trump stands to benefit. In the betting markets, the odds on him taking the nomination have shortened in the past couple of weeks. Trump is still the second favorite, behind Rubio, but some online bookmakers have lowered his odds to two to one, which implies that he has a thirty-three-per-cent chance of winning. (The most common odds on Trump winning are nine to four, which suggests a slightly lower probability of victory: thirty-one per cent.) These numbers shouldn’t be taken too seriously: the amount of money being staked on the race is relatively small, and bettors, like everybody else, are making guesses. But the shortening of Trump’s odds reflects a reassessment of his chances among people who follow politics closely.

It also reflects his continued strength in the polls. At the national level, according to the Huffington Post’s poll average, Trump is at 38.6 per cent; Ted Cruz is in second place, at 16.3 per cent; and Rubio is in third place, at 10.7 per cent. There is some debate about how to interpret these numbers. Some commentators, such as FiveThirtyEight’s Nate Silver and his colleague Harry Enten, have argued that we should concentrate on the state polls because the national surveys, at this stage, don’t have much predictive power. Sam Wang, of the Princeton Election Consortium, disagrees with this analysis. In a post published earlier this week, he wrote of Trump, “If 2016 were to follow the pattern of past elections, he would be the most likely nominee.”

Since the dynamics of the race will be determined in the first four states to vote—Iowa, New Hampshire, Nevada, and South Carolina—I tend to agree with Silver and Enten, although I wouldn’t entirely dismiss the national numbers. Comparisons of Trump to Rudy Giuliani, who led the national G.O.P. polls for much of 2007, only to come a cropper in Iowa and New Hampshire, aren’t very persuasive. A few weeks before the 2008 Iowa caucus, which took place in early January, Giuliani’s lead in the national polls was fast disappearing, and Mike Huckabee was catching up with him. Trump’s lead in the national polls appears to be holding steady.

More importantly, he is also doing well in the early-primary states, although not quite as well as he is in the national polls. I’ve already mentioned New Hampshire, where, according to the Huffington Post’s poll average, he has a thirteen-point lead over Rubio. In Nevada and South Carolina, he has a fourteen-point lead over Cruz. In Iowa, it is different: he is trailing Cruz by three percentage points.

What happens in the Hawkeye State is important. In one Trump-failure scenario, Cruz defeats him in Iowa, stopping Trump’s momentum, and then someone else—Rubio or Christie, perhaps—rallies and finishes in first place in New Hampshire, effectively finishing him off. Unfortunately, no Iowa poll has been published since before Christmas, so it’s hard to know what’s happening there right now. It’s also unclear how good a job Trump has done in building up his Iowa ground operation, which is key in a state where voters are forced to spend three or four hours at the caucus. Until we get more clarity about these factors, it’s unwise to make any predictions.

That said, I wouldn’t be surprised to see Trump beaten there by Cruz, who has practically moved to Iowa and has thousands of volunteers there. If Cruz did emerge victorious, the issue would then be whether Trump’s defeat would feed over to New Hampshire. Given that for years Trump was supportive of abortion, and that he has a general reputation as a social liberal (by Republican standards), he could argue that coming second in a state where roughly sixty per cent of G.O.P. primary voters are born-again Christians was a good result. On the other hand, he has staked a lot on being a winner. How would he handle a setback?

Winning New Hampshire handsomely would put Trump back on track, but with the campaign then moving to South Carolina and Nevada it would also matter a lot who came in second and third. To establish themselves as credible alternatives to Trump and Cruz, the four establishment candidates—Rubio, Christie, Bush, and Kasich—all need to do well in New Hampshire. That is a mathematical impossibility, however. At least one of these four, and possibly two or even three, could see his hopes end in the Granite State.

Right now, Christie, who has spent a great deal of time there, appears to have the most momentum of the four. Two months ago, he was polling at five per cent in the New Hampshire polls. Today, according to the Huffington Post poll average, he has risen to thirteen per cent. Rubio, too, has seen his support climb, although not very dramatically. Not surprisingly, the exchanges between the Rubio and Christie campaigns are getting bitter, with the New Jersey Governor this week accusing the Florida Senator of trying to "slime his way to the White House.” Bush and Kasich haven’t given up hope of emerging from New Hampshire with new life, either. The new Public Policy Polling survey shows them both within five points of Rubio.

In short, it is all still to play for. The next televised debate will take place in South Carolina, on January 14th, and there will be another one, in Iowa, two weeks later, just four days before the caucus takes place. Between now and then, a lot more polling data will be published, too. I’ll try to keep you updated.