Donald Trump campaign manager Corey Lewandowski’s abrupt firing Monday came down to a battle of ultimatums.

And ultimately, Lewandowski lost.

Paul Manafort, the veteran operative who since March has been amassing influence inside Trump HQ, recently telegraphed through third parties he would be gone in 48 hours if Trump didn’t oust Lewandowski, who'd run his campaign from the outset. Manafort was fed up with battling Lewandowski and let the campaign know the two of them "just couldn't get along."

From there, it became a family affair. Trump’s daughter Ivanka and her husband Jared Kushner didn’t want to lose Manafort, believing him to be the more experienced hand to guide the campaign into the general election.

They convinced Trump to keep him – and the only way to do that, given Manafort’s terms, was to dump Lewandowski.

Faced with a choice, Trump chose Manafort.

This account was relayed to Fox News by a campaign source. The details shed light on arguably the biggest staff shake-up of the 2016 cycle.

Despite the shock of Trump parting ways with Lewandowski, one of his closest and most loyal advisers, just weeks before the convention, in some corners the decision was not so surprising.

The former conservative activist played a central role in daily operations, fundraising, and Trump's search for a running mate, but Lewandowski's aggressive approach also fueled near-constant campaign infighting that complicated Trump's shift toward the general election.

Another Trump campaign official, Michael Caputo, resigned Monday afternoon over a tweet he sent out earlier in the day about Lewandowski's firing, a campaign source told Fox News.

Caputo tweeted "Ding, dong, the witch is dead" shortly after news about Lewandowski broke. Accompanying the tweet was a photo from the "Wizard of Oz," showing the feet of the Wicked Witch of the East protruding from under a house.

Campaign spokeswoman Hope Hicks confirmed Caputo is no longer with the campaign.

Reached on Monday by The Associated Press, Lewandowski deflected any criticism of his approach, pointing instead to Manafort.

"Paul Manafort has been in operational control of the campaign since April 7. That's a fact," Lewandowski said, declining to elaborate on his dismissal.

In a subsequent interview with CNN, Lewandowski repeatedly said he didn’t know why he was fired. But he said working for the campaign was “an honor and a privilege” and he “wouldn’t change one second.” He also claimed there was no animosity in the relationship with Manafort.

A person close to Trump told the AP that Lewandowski was forced out largely because of his poor relationship with the Republican National Committee and GOP officials.

On Capitol Hill, a Republican congressional aide close to pro-Trump lawmakers told Fox News the campaign did not inform members of Congress of the Lewandowski departure. Still, some sources said they were not surprised by the move and had been given the impression there would be a pivot soon to the general election, involving a potential staffing change.

Fox News is told that Trump’s children ultimately convinced the presumptive Republican presidential nominee to lose Lewandowski – an effort preceded by the tensions between Manafort and Lewandowski.

Manafort was originally brought on in March to help the Trump campaign’s delegate operation. He was later promoted to the role of campaign chairman – and will now take over as campaign manager, Fox News is told.

“He’s the campaign chairman, so yeah – he’s the person in charge,” Trump senior adviser Barry Bennett told Fox News.

Whether the ouster is simply an effort to smooth over rifts inside the Trump campaign or signals a major shift in strategy remains to be seen.

Bennett downplayed the notion that there would be any dramatic changes, but suggested Trump would be talking more about the issues in the weeks ahead.

Republican National Committee Chairman Reince Preibus told Fox News' Greta Van Susteren in an "On The Record" interview he thought the staff change was a "new direction" for the Trump campaign.

"I see a pivot and seriousness to the general election," he said.

Lewandowski has long been a controversial figure in Trump's campaign, but benefited from his proximity to the presumptive Republican nominee. He traveled with Trump on his private plane to nearly every campaign stop, giving him more direct access to the businessman than nearly any other campaign staffer.

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

Spokeswoman Hope Hicks said in a statement: "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. The campaign is grateful to Corey for his hard work and dedication and we wish him the best in the future."

The decision to part ways followed a rough patch for Trump at a time when he had an opening to crank up his general election operation as presumptive Democratic nominee Hillary Clinton was still fighting to fend off Bernie Sanders. Instead, Trump’s poll numbers against Clinton slipped, as Trump has found himself caught up in several controversies over his own comments – in turn stoking tensions with other top Republicans.

Aside from the controversies that have hung over the Trump campaign in recent weeks – including his comments claiming a judge is biased against him in the Trump University case because of his Mexican heritage; his renewed calls for a Muslim immigration ban; and his decision to revoke credentials for The Washington Post – the campaign is also entering a new and arguably tougher phase as Democratic groups start spending big against him.

Clinton and her Democratic allies have invested at least $41 million in commercials in crucial states such as Ohio, Florida and Nevada over the next six weeks. Those messages will be echoed by hundreds of Clinton workers in those same states and amplified by President Obama and other top Democrats.

Vice President Biden was also delivering an anti-Trump speech Monday.

Fox News’ John Roberts and The Associated Press contributed to this report.