"Lyin' Ted." "Crooked Hillary." How about "Presidential" Donald?

With a general election in his grasp, the Republican presidential front-runner who tarred his rivals Ted Cruz and Hillary Clinton as a liar and a crook now seems to be rebranding himself.

At least 20 arrested as supporters, opponents clash 0:50

"It's very easy to be presidential," Donald Trump told reporters in Manhattan, after sweeping five Eastern state primaries on Tuesday. "I'm not playing a part."

But it's a public image that's proving elusive. So elusive, in fact, that some of Trump's former strategists question whether a "presidential" Trump persona really exists beyond brief performances at victory rallies and formal speeches like his foreign policy address this week.

"That's not the type of person he is," says Stephanie Cegielski, who was contacted by the Trump team in 2015 for her public-relations expertise, and also formerly served as communications director for the pro-Trump SuperPAC Make America Great Again.

"I think he's so steeped in his bombastic persona that it will be difficult for him to stick to a presidential, canned message," she said.

As the Trump campaign shifts into general election mode, the former reality TV star is facing a clash of personalities.

Hillary Clinton and Ted Cruz, seen here during the Iowa primary, have both been the targets of name-calling by Donald Trump. (Associated Press)

Leaked recording

The challenge going forward, according to political strategists, will be how to balance the dignified obligations of the nation's highest office with the blustery showmanship that elevated his candidacy.

Trump is not handled, Trump is not coached, he is not programmed. He is genuine. He is his own man. - Roger Stone, Republican strategist and Trump supporter

Cegielski says she recommended Trump not stray from standard stump speeches. She suspects his advisers would prefer that too.

Trump may have been told by his new campaign adviser Paul Manafort to tone down the rhetoric and embrace a more dignified manner. Whether that's sustainable remains an open question.

Cegielski has her doubts.

"I'm not convinced that Trump can keep up that tone of playing nice in the sandbox," she says. "He has a very distinct and direct personality, and isn't terribly keen on being told how to present himself."

A leaked recording from a private briefing fuelled rumours that a more mainstream Trump might emerge soon.

In the recording, obtained by the news outlet Politico, Manafort assures Republican National Convention members that the brash real estate mogul has been "projecting an image," and that "the part that he's been playing" would mature appropriately for the general election.

The comments reportedly incensed the candidate.

Trump bristled at the suggestion that he's only presenting himself as a national political leader, insisting he has the diplomatic chops to function effectively in the Oval Office.

"Look, I'm not changing," he told reporters in New York on Tuesday. "I went to the best schools. I'm, like, a very smart person, I'm going to represent our country with dignity, and very well. I don't really want to change my personality, it got me here."

During a recent rally, Donald Trump mocked the table manners of rival and Ohio Gov. John Kasich, calling him 'disgusting.' (Pablo Martinez Monsivais/Associated Press)

Dangerous game

Even so, he brought a different temperament to Washington on Wednesday. In a measured tone, he delivered a foreign policy speech urging "clear-eyed" approaches to terrorism, while leaning on an aid that has been rarely used in his campaign so far — a Teleprompter.

"We should seek common ground based on mutual interests," he said, regarding relations with Russia, while ditching some of the more hawkish barbs he's used on the stump.

There were stumbles. His flubbing of the pronunciation of "Tanzania," for example.

But it showed an uncharacteristically restrained Trump compared to earlier in the week.

Just two days before the sober foreign policy speech, Trump was cheered on at a Rhode Island rally as he mocked John Kasich's table manners, pantomiming the Ohio governor chowing down on breakfast at a Pennsylvania diner.

"He's shoving it in his mouth," Trump said, bringing an invisible fork to his mouth and smirking. "It's disgusting."

There was at least one other moment in which Cegielski felt she was watching a more stately Trump.

"Following the New York primary, there was a definite shift in tone," she said. There were no references to "Lyin' Ted," only remarks addressing "Senator Cruz."

The danger in trying to remake Trump lies in his appeal as an off-the-cuff, say-anything personality, warns Steve Jarding, a public policy lecturer with the John F. Kennedy School of Government at Harvard.

"You never try to reinvent yourself. People see right through it, and they think politics is fraudulent enough," Jarding says.

"So it's a very dangerous game they're playing to say this Donald Trump is somebody other than the Donald Trump we've been watching for the better part of the year."

Donald Trump walks past a Teleprompter after delivering his foreign policy speech on Tuesday. (Jim Bourg/Reuters)

Not handled, coached, programmed

In an open letter published last month, Cegielski wrote of a guiding principle within the campaign that was used as a mantra: "Let Trump Be Trump."

Washington-based Republican strategist Roger Stone believes there's little sense in shifting strategies now. Not when delegate math favours Trump possibly winning a first-ballot nomination at July's Republican National Convention.

Stone, a long-time friend of Trump's and a former strategist on his campaign, says he knows the billionaire real estate magnate can conduct himself appropriately.

But he doesn't buy that a more "cerebral" Trump exists in private, as former political rival Ben Carson suggested last month, or that voters will soon meet a version of Trump that's closer to a conventional politician.

"There is only one Trump, and Trump marches to his own drummer," Stone said. "Trump is not handled, Trump is not coached, he is not programmed. He is genuine. He is his own man. I think a lot of political strategists and consultants are used to having a client who is malleable."

Delegate hunting in California

Trump is scheduled to deliver a lunchtime keynote speech today for the California Republican Convention, and will be joined by his rivals for the nomination Cruz and John Kasich. Thousands are expected at what could be one of the biggest Republican conventions in the Golden State in decades.

It will give Republican voters another look at how the three competitors engage with the same crowd. It also offers Trump a chance to target delegates and persuade them that he is presidential material.

For his part, Stone rejects the logic that a presidential hopeful needs to adopt a more traditionally political demeanour. Trump has changed the game too much to start playing along now, he says.

"The anger in the country is so palpable, I'm not sure it calls for a change in tone," he says. "He's not a stiff, he's a truth-teller and a showman. And politics, as well as being educational, has to be interesting. When you're not putting any interesting or provocative proposals out there, the voters get bored."

"One thing you can say about Trump," Stone added, "he's never boring."