While the most significant U.S political event in 2016 will be the presidential election in November, the lead-up could be just as intriguing in that the fate of Republican Donald Trump's controversial and surprising candidacy should finally be resolved.

On the Democratic side, unless something unforeseen happens, former senator and secretary of state Hillary Clinton should easily wrap up her party's presidential nomination, meaning all the real drama will take place in the Republican race, as it has been for some months now.

"That's what's going to swallow all the political oxygen," says Matthew Baum, professor of public policy at Harvard University's John F. Kennedy School of Government.

In fact, most of that oxygen has already been gobbled up by Trump, the real estate mogul and former reality TV star, who, despite a slew of controversial statements, has befuddled prognosticators by continuing to lead in the polls.

In this pre-primary period, the GOP race has been looking like a contest between Trump, Texas Senator Ted Cruz and Florida Senator Marco Rubio.

And with neurosurgeon Ben Carson's campaign imploding, as witnessed by the resignation of key members of his team, including his campaign manager, last week, New Jersey Governor Chris Christie is now said to have a shot at being the dark horse. 

This is why so much attention will be focussed on the Iowa caucuses on Feb. 1, which kick off the presidential nominating contest, culminating in a party convention in Cleveland in July. 

Iowa the first test

"Iowa's going to be interesting, and it will be the first test for us to see whether he [Trump] can turn his supporters into voters," said Tom Bevan, co-founder and executive editor of the RealClearPolitics website. 

Currently polls show Cruz slightly ahead of the former host of The Apprentice in Iowa, and a second- or even third-place finish by Trump won't necessarily shock most observers. 

Historically, Iowa  hasn't exactly been a strong predictor of the eventual Republican nominee, observes Geoffrey Skelley, a political analyst at the University of Virginia Centre for Politics. Going back to 1976, there have been seven contested Iowa caucuses on the GOP side, and in just three of those did the eventual nominee triumph, he said.

"Trump has consistently highlighted the fact that he's a 'winner,' so the question is, would a loss in Iowa seriously damage the winning veneer of his candidacy? That's difficult to say."

Campaign 2016 Abortion Divide

Texas Senator Ted Cruz, a Tea Party favourite, is hoping to sweep the Iowa caucuses on Feb. 1 and so slow the Trump juggernaut. (The Associated Press)

A significant loss, though, could affect him psychologically, suggests political analyst Stuart Rothenberg, author of the highly regarded Rothenberg Political Report.

"How does he deal with the fact that not everybody loves him? Is he then looking at a series of defeats and figures 'I don't want this, I don't want to risk two losses.'"

That's why the following primary a week later in New Hampshire, where polls currently have him leading the state by double digits, may prove more significant. 

"The expectations are high there and he needs to meet them," said Bevan. If he wins by only a narrow margin, "I think that's going to make it really interesting for Trump in how he responds to that and how it will affect his overall campaign and strategy."

Mind you, if he loses both Iowa and New Hampshire, that would deal a severe blow to his candidacy, especially having consistently led in New Hampshire for so long, Skelley said.

Titanic clash in South Carolina?

Should Cruz win Iowa and Trump New Hampshire, that could set up a titanic clash in South Carolina's primary on Feb. 20.

The winner of the South Carolina contest could use that as a jumping off point to win a large number of primaries on March 1 throughout the South, Skelley suggests.

"It would be fairly unlikely for [Trump] to win South Carolina if he wins neither of the first two contests. If that happens, I think we could safely say his star has burnt out."

If Trump remains a strong contender, though, it will be interesting how the Republican party, and its so-called establishment, reacts. 

Cruz, who is considered a more polished alternative to Trump, and who looks poised to make a strong showing in Iowa, South Carolina and on Super Tuesday — with its 12 state primaries on March 1 — is also loathed by much of the party establishment.

Part of the problem for the GOP establishment is that its support is fractured, Skelley says. While some back former Florida governor Jeb Bush, others support Christie or Ohio Governor John Kasich, while a fair number are trying to rally behind Rubio.

GOP 2016 Rubio

Florida Senator Marco Rubio, campaigning in New Hampshire last month, is said to be gaining some so-called establishement support. (The Associated Press)

"Many of these candidates are pretty much all-in on New Hampshire. If they don't do well there, their candidacies may meet a quick end.

"If a couple of these candidates drop out shortly after New Hampshire, it could enable the establishment to rally around one candidate," Skelley suggests.

"The conventional wisdom at the moment is that Rubio will wind up being the de facto establishment candidate, though we'll see if that works out."

The Rubio campaign seems to be waiting to see where, among the first three states, he has a chance to break out, Rothenberg said.

And if he does well enough in those states, that will help establish his campaign in Florida — one of those winner-takes-all primaries, on March 15 — and possibly beyond.

Still, Rothenberg said that strategy seems somewhat reminiscent of the failed one employed in 2008 by former New York mayor Rudy Giuliani who decided to avoid fighting hard in the early primaries in the hope of cleaning up in the bigger states.

An early favourite to win the race, Giuliani never gained any real momentum.

"You got to win somewhere and you got to win sooner rather than later," Rothenberg says. "If you're not winning early, your supporters might just as readily go to somebody else who pulls up a surprise win."