Donald Trump has fired his campaign manager, Corey Lewandowski, in a shake-up designed to calm panicked Republican leaders.

Mr Lewandowski had been by Mr Trump's side since the beginning of his unlikely rise to presumptive Republican presidential nominee but he clashed with long-time operatives brought in to make the campaign more professional.

The former conservative activist played a central role in daily operations, fundraising, and Mr Trump's search for a running mate, but Mr Lewandowski's aggressive approach also fuelled campaign infighting.

Mr Lewandowsky has deflected criticism of his approach, pointing instead to campaign chairman Paul Manafort.

Glasgow Times:

He said: "Paul Manafort has been in operational control of the campaign since April 7. That's a fact."

Trump spokeswoman Hope Hicks described Mr Lewandowski's departure as a "parting of ways".

A source close to Mr Trump said Mr Lewandowski was forced out largely because of his poor relationship with the Republican National Committee and party officials.

The move came as Mr Trump faces continued deep resistance from many quarters of his party concerned by his contentious statements and his reluctance to engage in traditional fundraising.

Mr Trump was upset that so many Republicans such as House Speaker Paul Ryan and Senate Majority Leader Mitch McConnell were reluctant to support him, and partially blamed Mr Lewandowski, according to the source.

"Firing your campaign manager in June is never a good thing," said veteran Republican operative Kevin Madden. "The campaign will have to show dramatic changes immediately on everything from fundraising and organising to candidate performance and discipline in order to demonstrate there's been a course correction. Otherwise it's just cosmetics."

Mr Lewandowski has long been a controversial figure in Mr Trump's campaign, but benefited from his proximity to the presumptive Republican nominee.

Often mistaken for a member of the candidate's security team, he travelled with Mr Trump on his private plane to nearly every campaign stop, giving him more direct access to the businessman than nearly any other campaign staff member.

He was a chief promoter of the idea that the best campaign strategy was to "Let Trump be Trump". Mr Lewandowski frequently dismissed the notion that Mr Trump needed to hire more experienced political hands, spend on polling and sophisticated data operations, and moderate his rhetoric as he moved towards the general election.

Glasgow Times:

That approach clashed with seasoned operatives hired in recent months.

Minutes after news of Mr Lewandowski's departure was announced, Trump aide Michael Caputo tweeted: "Ding dong the witch is dead!". He also included a link to the song from the film, The Wizard Of Oz.

Mr Lewandowski was charged with misdemeanor battery in the spring for an altercation involving a female reporter during a rally. The charges were later dropped. Mr Trump defended Lewandowski throughout the episode and repeatedly framed his own actions as a sign of loyalty and a demonstration that he would not give in to outside pressure.

"Folks, look, I'm a loyal person," Mr Trump told voters at the time.

"It's so important," he said of loyalty in a subsequent interview. "And it's one of the traits that I most respect in people. You don't see it enough."

Yet Mr Lewandowski's approach within the campaign sparked intense criticism from experienced Republican operatives inside and outside of the campaign.

The move comes a day before Mr Trump is to attend a major New York City fundraiser, organised by long-time Republican financier Woody Johnson. Mr Trump will spend part of Tuesday and Wednesday at finance events in his home city.

Many of the top Republican fundraisers had encountered turbulence between worried donors and a campaign manager who did not seem fully onboard with the idea that Mr Trump and the party needed to buckle down and raise the money needed to build a robust general election operation.

Republican strategist Ryan Williams, a frequent Trump critic, said that Mr Lewandowski's dismissal "is the first major public admission from Donald Trump that his campaign is not going well".

"This shows donors, activists and party officials that he is willing to make significant changes, even if it means parting ways with a trusted political aide," Mr Williams said.

"Now Trump needs to demonstrate that he is willing to change his own approach by toning down his rhetoric and becoming a more disciplined general election candidate."