Donald Trump has parted ways with his campaign manager and close ally, Corey Lewandowski.

While some campaign sources tell NPR the split was "mutual," another described it as a "firing" and a "summary execution." The source said the news was unwelcome for Lewandowski at the weekly Monday staff meeting. The "weekly Monday morning family meeting went awry for Corey," the source said.

The move appears to be a reaction to the presumptive GOP nominee's sagging poll numbers and weeks of difficulty as he prepped for a tough general-election fight with Hillary Clinton. Trump was set to hold a call with his advisers and staff Monday morning in the wake of Lewandowski's departure.

Officially, the campaign tried to put a good face on it. "The Donald J. Trump Campaign for President, which has set a historic record in the Republican primary having received almost 14 million votes, has today announced that Corey Lewandowski will no longer be working with the campaign," spokeswoman Hope Hicks said in a statement. "The campaign is grateful to Corey for his hard work and dedication and we wish him the best in the future."

Lewandowski has been with Trump since he began his presidential run, managing his shoestring operation. But as Trump has moved into the general election, a more traditional campaign structure largely managed by Paul Manafort, a former Ronald Reagan aide, has emerged. Within the campaign, Manafort and Lewandowski have been seen as competing forces. A campaign source told NPR that Trump previously had liked the competitiveness between the two.

"[Corey] knew there was a battle brewing. I am certain he thought he would win," one campaign source told NPR.

Lewandowski, though, has been a source of controversy himself. There were accusations — and a battery charge that was later dropped — following a confrontation with a former reporter for Breitbart News in which Lewandowski was seen on video appearing to grab her arm. The news of his ouster on Monday was first reported by the New York Times.

Even though Trump effectively clinched the Republican nomination more than six weeks ago, his campaign has yet to prepare for the usual rigors of a general-election campaign — hiring top staff, preparing a rapid response and communications team and beginning fundraising and building a data-analytics operation.

Instead, Trump has continued to swirl in controversy, targeting a judge presiding over the Trump University fraud case by accusing him of bias because of his Mexican heritage. He doubled down on his Muslim immigration ban and expanded it after last week's deadly shooting at a gay nightclub in Orlando, Fla. He called for a ban on anyone coming to the U.S. from any country with a proven history of terrorism against the U.S. or its allies. He also made confusing comments on guns, initially saying that if clubgoers had been armed, the shooter could have been stopped. He walked that backafter even the NRA disagreed with him.

Lewandowski helped preside over Trump's unconventional primary campaign, bolstered by the billionaire businessman's sheer personality and ability to command the news cycles, dwarfing his GOP opponents. But in a general election, Trump hasn't been able to do the same.

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