Why Donald Trump could win the Republican presidential nomination

Washington: Billionaire businessman Donald Trump has in the past eight months defied his critics and proven his White House bid is not simply a surreal stunt.

To the shock of the political world, the 69-year-old onetime reality TV star's nomination to be the Republican presidential candidate is now a genuine possibility.

His populist campaign has morphed into a national protest movement against Washington elites and establishment "politicians."

He has rallied fiscal and social conservatives as well as moderate Republicans who could propel him to the nomination -- but the GOP trophy will depend on the behavior of other party rivals still in the race.

The crowded field shrank by one after Saturday's South Carolina primary slugfest, leaving five: Trump, Senators Ted Cruz and Marco Rubio, and two underdogs -- Ohio Governor John Kasich and retired neurosurgeon Ben Carson.

Trump has a solid support base of about 30-35 per cent of the Republican vote: He won New Hampshire with 35 per cent and South Carolina with 32.5 per cent. In national polls, he is averaging about 34 per cent support.

So long as the remaining votes are divided between other candidates, as occurred in the first three nomination contests, Trump appears unbeatable.

And from March 15, most states will award their delegates via the winner-take-all method, which would help Trump clinch the nomination before the Republican convention in July in Cleveland.

But if several others withdraw -- as Jeb Bush, the son of one president and brother of another, did Saturday after faring poorly in South Carolina -- voters could in theory elevate a challenger capable of uniting the Republican electorate against Trump.

"I do think Trump has a ceiling, probably around 40 per cent, and that he's not going to do much better than that," explained University of Massachusetts political science professor Brian Schaffner, who also directs the UMass Poll.

Trump might snag some voters from Carson, who is popular with evangelicals, should the doctor drop out, and he is likely to earn trickles of support from Bush and others who suspend their campaigns.

But Schaffner has studied surveys about voters' second, third and fourth choices, and has concluded that it's pretty black or white on Trump.

"Most of the people who don't support him really have no interest in supporting him," and the majority of those who had backed Bush or Kasich -- symbols of the establishment -- would switch allegiance to either Cruz or Rubio, he explained.

'A three-person race'

Trump has no patience or use for the calculations of such "geniuses," and who can blame him? He has defied expectations daily since last summer.

"They don't understand that as people drop out," Trump said on Saturday night, "I'm going to get a lot of those votes also."

Indeed, voters are hardly beholden to the prognostications of political experts. They may be more sensitive to personality traits than political platforms.

Trump's undisputable talent "is to keep the focus on him" and not necessarily his policies, generic as they are, said Timothy Hagle, a professor of political science at the University of Iowa.

America's political left has essentially anointed Trump a bona fide frontrunner.

"Nothing is certain in politics," wrote Josh Marshall, editor of web-based Talking Points Memo.

"But it's time to dispense with any faith-based logic that disputes the fact that Donald Trump is now the overwhelming favorite to win the Republican nomination."

Cruz, a champion of the religious right, is struggling to reach voters beyond his arch-conservative core, but he is determined to hang on.

Rubio nipped Cruz for second place on Saturday in South Carolina, consolidating his position as the mainstream darling.

"After tonight, this has become a three-person race, and we will win the nomination!" Rubio told cheering supporters.

There are indeed some obstacles in Trump's path, notably involving his campaign organization.

"Can he expand his campaign to more than one state at a time?" Hagle asked.

Eleven states across the country will cast ballots in Republican nominating contests on "Super Tuesday" (March 1), and Trump's campaign team has fewer staff and volunteers -- and less ground experience -- than his well-stocked rivals.

There is also the scenario in which Trump, Cruz and Rubio remain in the race until the July convention, with none having managed to secure an absolute majority of delegates -- 1,237 out of the 2,472 available.

Should that unfold, after a first round of voting, delegates would be released from their initial commitments and could vote for the candidate of their choosing in the second round.

Woe to whoever predicts the outcome in that scenario.