Donald Trump can be stopped from winning the Republican nomination - but only if things happen, and fast

Thank heavens. After months of armchair strategising, of who’s-up-and-who’s-down polls, and of politics as reality TV, America’s presidential election season is properly under way. This Monday night, the decent but usually obscure Midwestern state of Iowa holds its caucuses, in which the first votes that count will be cast.

And with all due respect to Hillary Clinton and Bernie Sanders, one question overshadows every other. Can anyone stop Donald Trump from winning the Republican nomination? The short answer is still yes. But several things have to happen, and quickly.

Objectively, we probably shouldn’t get so fussed about Iowa. A candidate needs the support of 1,237 delegates to be nominated at the Republican convention in July. Iowa provides only 30 of them, to be allotted on a proportional basis (and New Hampshire, whose primary follows eight days later, accounts for only 23).

Nor is Iowa a glittering advertisement for participatory democracy. In 2012, just 20 per cent of the states’s registered Republicans took part in the caucuses – small wonder when the process can last up to two hours. Oh, yes, and a big snowstorm is forecast for Monday night, making such an evening out even less enticing. But Iowa has disproportionate influence simply because it goes first. And Trump is favourite to win the caucuses.

So a first thing has to happen: Trump’s support in the polls doesn’t translate into caucus votes. That is entirely possible. His campaign has been fantastic entertainment, fusing politics and showbusiness as none before it. Far more than his rivals, Trump instinctively understands TV. Bombastic, narcissistic and a bully he may be, but you can’t take your eyes off the man. His giant rallies have been the best free shows around.

Nor does his non-attendance at Thursday’s final pre-caucus debate seem to have done him any harm. Even in absentia he loomed over proceedings. His rivals failed to use the unaccustomed limelight to make compelling cases for themselves as the anti-Trump. And, by staying away, he avoided putting his foot in it a few days before the vote – not that putting his foot in it has hurt candidate Trump.

Nonetheless, no matter how high his TV ratings, people actually have to caucus for him. What matters, especially in Iowa, is a candidate’s “ground game” on the night, whether he or she can get supporters to the private homes, church halls and gyms where the caucuses take place. The strength of Trump’s ground game remains to be seen.

But suppose he does win in Iowa, beating that other demon of the establishment, Texas senator Ted Cruz (who was generally deemed a loser on Thursday evening). It would be a pretty remarkable feat – that a man of the sketchiest conservatism, more conversant with New York night spots than with the Nicene creed, thrice married and twice divorced, and a past supporter of abortion rights, wins in a state where evangelicals and self-described “strong” conservatives dominate the Republican electorate.

It would be proof that Trump’s message – secular, populist and intolerant, – reaches not only disaffected white voters who feel ignored by the Republican hierarchy, but also religious conservatives. It would set him up perfectly for the 1 March “Super Tuesday” set of contests across the South, where those two constituencies are paramount.

If the real-estate mogul does win Iowa, then it is a racing certainty that he will be victorious in New Hampshire as well, where he has a much more commanding lead. At that point, the picture looks extremely good for Trump: since 1972, five of the six men who’ve pulled off the Iowa/New Hampshire double in contested races have gone on to be their party’s nominee.

To prevent this, something else has to happen: a rapid winnowing of the Republican field. One of the reasons Trump dominates is that the opposition is so fragmented. There’s Cruz, of course, but also nine others, including four so-called “establishment candidates” who are spending more time and money fighting each other than on attacking Trump.

Add together the support of these four – Florida’s Senator Marco Rubio, the state’s former governor Jeb Bush, and governors Chris Christie of New Jersey and John Kasich of Ohio – and you get pretty close to Trump’s figure. Persuading them to drop out, however, will be quite another matter, given all the pressure that will be exerted by the Republican top brass, donors and party grandees.

If one of them does notably better in both Iowa and New Hampshire (Rubio right now looks the best bet) then just maybe the others will fall on their swords for the good of the party; or, more realistically, for want of money for the campaign ahead. But even if he just continues to bump along in mid-single digits, can you imagine Jeb Bush ending his candidacy when he’s still got $50m to spend? It’s tough.

Without this winnowing, however, Trump will surely continue his hostile takeover of one of America’s two great parties. The Republican establishment has lost control of proceedings. Faced by a billionaire beholden to no one, its endorsements, its threats and its fund-raising levers simply don’t matter.

Trump hasn’t received a single high-ranking endorsement (unless you count that of the quasi-pariah Sarah Palin). As for money, he’s got more than enough of his own. As for the traditional media pillars of the party – Fox News, of course, but also conservative magazines such as The Weekly Standard and The National Review – Trump basically ignores them.

The modern Republican Party has prided itself on being the repository and formulator of conservative principles. Donald Trump is tearing up the rule book of what it means to be conservative, and the party can do nothing about it. Only the voters can, if they so choose. But will they? That’s why all eyes will be on Iowa on Monday night.