BILLIONAIRE businessman and reality TV star Donald Trump took another step towards the White House on Wednesday, as analysts warned a Trump presidency would be a “disaster” for Australian-US relations.

Australian National University political analyst Dr Norman Abjorensen yesterday said: “Even the most impartial observer would think Donald Trump as president is a little bit scary.”

Mr Trump scored victories in three states on Wednesday, including the big-prize of Florida, as he continued his outspoken and controversial march to the Republican presidential nomination.

media_camera US Republican presidential candidate Donald Trump / Picture: AP

Dr Abjorensen said Mr Trump might look a lot different if he won the keys to the White House.

“It is too early to say what he would be like as president because in order to get the nomination you have to take an extreme position,” Dr Abjorensen said.

“He has been trying to rouse the party faithful. Once he has the nomination he would be likely to swing back to a more moderate position.

“I think we would be seeing a more moderate and chastised Donald Trump in the White House, if he got there.”

Lowy Institute executive director Dr Michael Fullilove warned: “The words ‘President Trump’ should give Australians pause.

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“Mr Trump reflects few of the values that have made America great. And judging from his speeches, he fails to see the advantages that flow to his country from being at the centre of the global liberal order.”

He said a Trump victory would also undermine the ANZUS security alliance.

“He seems positively allergic to Washington’s military alliances, which is a problem for a US ally such as Australia,” said Dr Fullilove.

Associate Professor Brendon O’Connor from Sydney University’s US Studies Centre said that if Mr Trump became president then “all bets are off regarding US Australia alliance”.

media_camera US Democratic presidential candidate Hillary Clinton / Picture: AP

He questioned whether allies would be prepared to take part in military exercises if America had a commander in chief who was more likely to escalate a situation, such as a friendly fire accident, rather than seek a diplomatic solution.

He said Mr Trump’s isolationist views on trade and migration were “an absolute disaster”.

“This is the type of talk you would expect from someone in the 1930s. He is an egomaniac who thinks he can solve all sorts of global problems but what happens when that is not the case? Will he escalate the situation?” he said.

media_camera Cartoonist Warren Brown’s view.

media_camera Australian National University political analyst Dr Norman Abjorensen says: “Even the most impartial observer would think Donald Trump as president is a little bit scary.”

TRUMP ON TOP, BUT IT’S NOT QUITE DON JUST YET

Anna Caldwell in New York

DONALD Trump has stormed another three states to rack up a delegate lead his competitors will struggle to beat, however a major defeat in the key contest of Ohio last night paved the way for a contested convention in July.

Mr Trump easily won North Carolina, Illinois and thrashed establishment favourite Marco Rubio in his home state of Florida, scooping the biggest prize so far of the contest and forcing the moderate to quit the race.

But a loss in the winner-take-all state of Ohio to moderate John Kasich — who is coming last in the race — could deprive Mr Trump of crucial delegates needed to secure the nomination in his own right.

media_camera How the Republican race stands at the moment.

media_camera How the US Democrats race stands

As Mr Rubio bowed out of the contest last night, he laid foundations for a future presidential bid in a rousing speech about optimism and unity, channelling Barack Obama’s breakout 2004 address.

Mr Rubio’s exit changes the dynamics of the race, leaving Mr Kasich — a man who has won only his home state — the sole moderate option against frontrunner Mr Trump and tea party favourite Ted Cruz.

On the Democratic side, Hillary Clinton last night sharpened her lead over opponent Bernie Sanders, clocking big wins in Florida, Ohio, Illinois and North Carolina.

The wins were a blow to Mr Sanders who had staked his path to the nomination partly on winning blue-collar Ohio, but fell short of repeating the upset he staged in Michigan last week.

It’s a much clearer contest now than the Republican fight, which looks to be a three-horse race to the party’s July convention.

media_camera Senator Ted Cruz sits on 394 delegates, well behind Trump’s 619. Picture: AP Photo/David J. Phillip

A winner needs to amass 1237 delegates to claim the nomination before the convention.

With some delegates from last night’s contest still to be divided, Mr Trump was hovering at 619, ahead of Mr Cruz on 394 and Mr Kasich on 136.

Even a substantial frontrunner cannot claim the title without reaching the magic 1237, instead opening the door for the establishment to conduct a series of ballots at the convention to select the nominee.

Mr Trump, at a plush campaign event at his Mar-a-lago residence last night urged his party to get behind him: “We have to bring our party together. We have to bring it together. We have something happening that actually makes the Republican party probably the biggest political story anywhere in the world.”

media_camera Senator Marco Rubio dropped out of the race after losing his home state of Florida. Picture: Angel Valentin/Getty Images/AFP

Mr Trump also name-dropped his favourite Australian golfer Adam Scott, referring to how he’d been watching Scott play when negative anti-Trump ads interrupted his viewing.

Mr Cruz was last night nipping at Mr Trump’s heels in Missouri, but had no clear lead in any state.

Mr Cruz focused his attack on new threat Mr Kasich, saying it was only himself and Mr Trump who had a path to the nomination.