Donald Trump’s campaign manager Corey Lewandowski is to leave his job.

A campaign spokeswoman said Corey Lewandowski would no longer be working on it and said the team was grateful to him “for his hard work and dedication”.

The exact reason for Corey Lewandowski’s departure is not yet clear but sources close to Donald Trump have told media he was fired.

Corey Lewandowski oversaw Donald Trump’s unlikely triumph in the primary contests.

His departure comes as Donald Trump faces strong resistance from senior members of his own party over his strident tone and his hard-line immigration policy.

Among Donald Trump’s critics is Speaker of the House and top-ranked Republican Paul Ryan, who appeared to leave the door open to a possible revolt at next month’s convention.

When asked on June 19 about reports that party delegates may rebel against voting for Donald Trump at the convention, he said: “They write the rules, they make the decisions.”

Donald Trump was criticized for his reaction to the Orlando nightclub shooting in which 49 people were killed.

Following the attack, Donald Trump repeated his pledge that the US should ban Muslims from entering the country.

Republicans also started to distance themselves from Donald Trump following his personal attacks against a Hispanic federal judge overseeing two lawsuits against him.

Donald Trump is likely to face Democrat Hillary Clinton in November’s election, and there were reports over the weekend that her campaign is way ahead in spending in the key swing states.

Corey Lewandowski has had a contentious relationship with the press. Earlier this year, he was charged with battery after allegedly yanking a female reporter out of Donald Trump’s way after a campaign event.

Donald Trump defended him throughout that incident, which concluded when the charges were dropped.

Following the news, one Trump campaign director, Michael Caputo, tweeted: “Ding dong the witch is dead.”

Corey Lewandowski did not get along with Donald Trump’s chief strategist Paul Manafort either, with sources telling the New York Times that he would try to block Manafort from hiring more campaign staff.

Donald Trump is suffering in political polls lately, with most voters viewing him as “strongly unfavorable”.

One of Donald Trump’s campaign staff member told NBC News that the campaign was not briefed on Corey Lewandowski’s firing and that right now there is “bedlam in the Trump campaign. No one knows what is happening”.