ABC Fact Check

Billionaire businessman Donald Trump has surged to the top of opinion polls as the preferred Republican presidential nominee in 2016, taking many pundits by surprise.

Mr Trump has also grabbed headlines with a series of attacks on illegal immigrants and other politicians.

But despite his frontrunner status and personal wealth, is a Trump presidency likely?

Here are some points to consider.

Few non-politicians have been elected president

If Donald Trump were to become president, he would be the first non-politician elected to the White Housesince Dwight D. Eisenhower in 1952.

General Eisenhower was an American hero, having been supreme commander of allied forces in Europe in World War II.

Herbert Hoover hadn't held elected office, but he was a highly respected administrator who had been appointed to a prominent government position during World War I and served as commerce secretary before winning the 1928 presidential election.

You might be wondering about former Hollywood actor Ronald Reagan, who was elected president in 1980 — but Mr Reagan had already been elected governor of California, serving two terms from 1967-1975.

Mr Reagan also stood unsuccessfully in the 1976 Republican primaries.

According to David Smith, lecturer in American politics at the US Studies Centre at the University of Sydney, first-time candidates face an uphill battle.

"Non-politicians lack deep support networks within the party, which are pretty crucial to winning the nomination," Dr Smith said.

John F. Kennedy was a sitting senator, Lyndon Johnson was a former senator and vice president, as was Richard Nixon.

Gerald Ford was appointed president and before that vice president, but he was a former congressman.

Jimmy Carter was a governor, George Bush Sr was vice president and former congressman.

Bill Clinton and George W. Bush were both governors and President Barack Obama was a United States senator, and former Illinois state senator.

Election analyst Sean Trende, who writes for the website Real Clear Politics says the chances of a non-politician being elected president are pretty slim.

"Simply put, the presidency isn't an entry level job," Mr Trende said.

"There's a reason we've only had a handful of presidents without a lengthy history of elected offices".

However Republican strategist Ford O'Connell, who is a former advisor to 2008 Republican presidential nominee John McCain, told Fact Check that while the odds of a non-politician being elected president aren't great, they are probably higher than at any time since General Eisenhower.

"The reason is that Americans are tired of politicians and Washington politics-as-usual, and a non-politician candidate could leverage that to his or her advantage," he said.

Inexperienced campaigners are prone to making gaffes

In October 2011 another colourful businessman reached the top of the polls as the preferred presidential nominee for the Republican Party.

Herman Cain, the former CEO of an American pizza restaurant chain, campaigned on a catchy tax policy he called "nine-nine-nine" — a 9 per cent personal income tax, 9 per cent business income tax and 9 per cent national sales tax.

But the "Cain Train" soon came off the rails when it became clear he knew little about foreign policy when asked if he agreed with Mr Obama on Libya.

Mr Cain searched for an answer, looked at the ceiling, then responded: "Got all this stuff twirling around in my head..."

Ron Nehring, former Republican Party nominee to be lieutenant governor of California, said such mistakes aren't surprising.

"First time candidates for president have missed out on the opportunities and training that comes from running for office before. As a result, they make a lot of rookie mistakes when they have he greatest number of people watching. This usually doesn't end well," Mr Nehring said.

In Mr Trump's case, he has already created controversy by calling illegal immigrants from Mexico "rapists", and a female lawyer who requested a break from a deposition to use a breast pump "disgusting".

Mr Trump also questioned the heroism of former Republican presidential nominee Senator McCain, who had been tortured as a prisoner of war in Vietnam, saying "I like people who weren't captured".

Media and voter scrutiny intensifies on frontrunners, so making gaffes and failing to look "presidential" is a real danger for "The Donald".

Successful politicians learn the art of covering themselves, saying things in way that minimise offence, Dr Smith said.

"Trump has spent his whole life getting publicity wherever he can, he has not learned this art and has no interest in doing so," Dr Smith told Fact Check.

However, Bill Schneider, a veteran presidential campaign journalist, says that trait is also central to Mr Trump's appeal.

"Trump says things you're "not-suppose-ta" say if you want to be a viable candidate."

In doing so Mr Trump comes across as unscripted and authentic, Mr Schneider said.

Money matters, but it's not everything

Mr Trump said during his announcement speech: "I'm using my own money. I'm not using the lobbyists. I'm not using donors. I don't care. I'm really rich."

The real estate tycoon claims a personal fortune in excess of $US10 billion, although analysis from Bloomberg puts his worth at $US2.9 billion.

In 2012, combined spending on the presidential election was around $US2.6 billion.

In 1992, businessman H. Ross Perot drew heavily on his fortune as founder of the tech giant EDS to pour $US63.5 million into his quixotic independent presidential campaign.

Mr Perot won almost 19 per cent of the popular vote, but failed to win a single state, much less the presidency.

In 1996 Mr Perot invested a more modest $US8.2 million into a second presidential campaign as a Reform Party candidate, this time only attracting 8.4 per cent of the vote.

Steve Forbes, the publisher of Forbes Magazine, ran for the Republican presidential nomination in 1996 and 2000.

He spent $US37.4 million on his first run and $US38.7 on his second, but didn't come even close to becoming his party's candidate.

Mr Trende from Real Clear Politics says candidates tend to self-finance because they don't have a widespread base of support, which is why they tend to lose.

And Dr Smith has doubts Donald Trump will want to dig too deep into his personal fortune.

"At this stage we really don't know how much money Trump has, let alone how much he's prepared to spend," Dr Smith said.

"Certainly it won't be in the $US2 billion range planned by the Clinton campaign, and in the primaries it won't be in the hundreds of millions that Jeb Bush is raising".

And according to Mr Nehring, by not being forced to ask people for money, Mr Trump is potentially not shoring up their support.

"Fundraising isn't just about money. It's about building a following of supporters. Many first time candidates who can fund their own campaign miss the opportunity to build a support base," Mr Nehring said.

Running as a third-party candidate.

If Donald Trump misses out on the Republican Party's presidential nomination, he has hinted he could run as an independent or "third party" candidate just as Mr Perot did.

"So many people want me to, if I don't win," Mr Trump said in an interview with political website The Hill.

"I'll have to see how I'm being treated by the Republicans," Mr Trump said. "Absolutely, if they're not fair, that would be a factor."

However third-party candidates, or ones who stand in the general election who are not the nominee of the two major parties the Republicans and the Democrats, have struggled to attract voters.

Some notable, but limited exceptions include; former Republican president Theodore Roosevelt, who after four years out of office stood as a progressive or "Bull Moose" candidate.

Teddy Roosevelt came second with 27 per cent of the vote, but really only helped elect rival Democrat Woodrow Wilson over Republican president William Howard Taft.

In 1968 segregationist southern Democrat George Wallace ran as an American independent and garnered 13.5 per cent of the vote.

The close election was won by Republican Richard Nixon.

As recently as 2000 however, a third party candidacy may have tipped an election.

Consumer advocate Ralph Nader won 2.7 per cent of the vote in a cliff-hanger election between Democrat Al Gore and Republican George W. Bush.

Mr Nader's 97,488 votes in the decisive state of Florida, which Mr Bush won by just 537 votes, probably cost Mr Gore the presidency.

But Mr Nehring, who is also for former Californian Republican Party Chairman said Mr Trump should have ruled out an independent campaign.

"Trump is making a strategic error by leaving open the possibility of running independently. It tells Republican primary voters he is less loyal to the team than they are. Big mistake," Mr Nehring said.

Strategist Ford O'Connell says while Mr Trump could take votes away from the Republicans if he runs a third party campaign, he says it isn't likely to happen because even for the billionaire businessman, the cost would be prohibitive.

Early opinion polls are not a great predictor

At publication, Donald Trump stands at just over 23 per cent in an average of recent polls, more than 10 points clear of nearest Republican rivals Jeb Bush and Scott Walker.

However, if polls mid-way through the year before a Presidential election were a reliable predictor, Hillary Clinton would have been up against Rudy Giuliani in the 2008 election rather than Mr Obama and Senator McCain, Michele Bachmann or Rick Perry would have battled Mr Obama in 2012 instead of Mitt Romney.

"Early polls aren't that accurate," Mr Trende said.

"Don't pay much attention to them for prognostication."

More telling might be a poll that shows Mr Trump also tops the list of candidates that Republicans say they would never support.

The same poll found Mr Trump performs worse than either Mr Bush or Mr Walker in a hypothetical match-up against likely Democratic nominee Ms Clinton.

American political history is littered with early frontrunners who soon stumbled: George Romney in 1968, Ed Muskie in 1972, Ted Kennedy in 1980, Gary Hart in 1988, Jerry Brown in 1992... the list goes on.

This article was originally published at ABC Fact Check