Donald Trump fired his controversial campaign manager Corey Lewandowski Monday, unleashing a major shake-up as he comes under pressure from his closest advisers – particularly his family members – to urgently reset his struggling presidential campaign. Lewandowski’s abrupt departure is the campaign’s most significant staff change to date and signals an acknowledgment from Trump that an overhaul is necessary ahead of the general election. Trump has suffered major setbacks since becoming the GOP’s presumptive nominee last month, coming under intense criticism from party leaders, major donors and rank-and-file Republicans for an array of issues – including his response to the terrorist attack in Orlando that killed 49 people. “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,” Trump spokeswoman Hope Hicks said in a statement Monday. “The campaign is grateful to Corey for his hard work and dedication and we wish him the best in the future.” RELATED: GOP donors rattled by Trump The decision to fire Lewandowski was made swiftly in a Monday morning weekly meeting with Trump’s family members, a Trump adviser said. In an interview with CNN’s Dana Bash, Lewandowski – asked why he was fired – said: “I don’t know. I don’t know the answer to that.” “But what I know is that what we’ve been able to achieve in this election cycle was historic,” Lewandowski said. “I had a nice conversation with Mr. Trump and I said to him, ‘It’s been an honor and a privilege to be a part of this,’ and I mean that from the bottom of my heart.” Lewandowski consistently pushed back on widespread reporting that his presence in the Trump campaign had grown toxic, even as he acknowledged that he is a “very intense person,” a perfectionist and a “straight shooter” – sometimes to his own detriment. And even without a formal role with the campaign, Lewandowski said he would do whatever he could to help Trump win the White House. He was also notably unapologetic: “I have no regrets as it comes to this campaign,” he said. Trump, speaking to Fox News’ Bill O’Reilly, in an interview set to air Monday night, praised Lewandowski, saying he was “really proud of him.” “He did a great job. But we’re gonna go little bit of a different route,” he told O’Reilly. Ivanka’s role Ivanka Trump, the candidate’s daughter, played a pivotal role in convincing Trump to take action against Lewandowski. She had been critical of Lewandowski for months and this was not the first time that she had leaned on her father to part ways with his top aide. Contributing to Ivanka Trump’s recent dissatisfaction with Lewandowski were intensifying tensions between Lewandowski and Ivanka Trump’s husband, Jared Kushner, an influential force behind the scenes. One source said rumors swirled that Lewandowski had attempted to plant negative stories in the press about Kushner – a final straw for Ivanka Trump. RELATED: 5 key Corey Lewandowski moments By this point, Eric Trump, Ivanka Trump’s brother, had already reached a breaking point with Lewandowski and expressed his frustrations about the campaign operations to his father, according to a senior campaign source. It was ultimately Ivanka Trump who sat down with her father on Sunday and convinced him to let Lewandowski go – even offering an ultimatum of sorts about her own continued involvement with the campaign, according to sources with knowledge of this conversation. The development suggests that Kushner – who is already involved in building a transition team for Donald Trump should he win the White House in November – could play an increasingly prominent role in guiding the Trump campaign. But Lewandowski on Monday denied that there were tensions between himself and Trump’s children, as well as Jared Kushner, telling Bash that he has a “great relationship with the family.” Lewandowski did not appear to know that the axe was about to drop: The firing was so sudden that he was on a call with Republican National Committee staffers Monday morning, just hours before his firing, according to one GOP source. Sources close to the campaign view Lewandowski’s ouster as a major reset for Trump’s campaign – as well as an explicit acknowledgment that things were not going well. Those closest to Trump worried that Lewandowski presented multiple problems for Trump. For one, they feared that Lewandowski was a hindrance to enlisting experienced, veteran strategists to join the campaign. There were also concerns that Lewandowski – with direct access to Trump’s ear – would get the candidate agitated on issues that ultimately “did not matter” to the campaign and feed some of Trump’s misguided instincts, two sources said. Toned down rhetoric Trump’s inability — and apparent lack of interest — in toning down his rhetoric going into the general election season has deeply troubled the party. There is widespread concern that without a dramatic course change, Trump will continue to be significantly outmatched by presumptive Democratic nominee Hillary Clinton on many fronts, including organization, communications and fundraising. The news, which was first reported by The New York Times, comes amid deep internal tensions that have roiled the Trump campaign. Lewandowski was well known for being fiercely loyal to his boss – he is even a Trump delegate from New Hampshire – and also deeply protective of his direct access to the candidate. This dynamic created a series of problems as the Trump campaign began to hire staffers and expand its operations, including when Trump enlisted veteran GOP strategist Paul Manafort earlier this year. The internal drama – which Lewandowski dismissed during his interview with CNN on Monday – was viewed as a huge source of distraction at a time when Trump needed to devote all of his campaign’s resources to preparing for November. With Lewandowski leading the campaign, Trump volleyed from one controversy to the next: unleashing attacks on Judge Gonzalo Curiel’s Mexican heritage and suggesting that President Barack Obama perhaps played a role in the Orlando massacre. Lewandowski encouraged this behavior, rather than prodding the candidate back on message, one adviser said. Amid all of these distractions, members of the Trump family, his friends, as well as Manafort, had been upping their efforts to convince Trump that Lewandowski’s guidance had grown harmful to the candidate and the campaign. Joining Trump’s family in making the case against Lewandowski was RNC Chairman Reince Priebus, according to one source familiar with the decision. Priebus has been personally making the case to Trump since late last week that Lewandowski had to go. RELATED: Trump clarifies armed club-goer stance after NRA split Some advisers hope the latest move will allow the campaign to ramp up more quickly by building out a communications team, a rapid response effort and by ramping up their political machine in battleground states, an adviser said. “This has not been a campaign, it’s been a concert tour,” the adviser said, adding this could be the turning point for the campaign to get more serious. A second adviser added a note of caution though, saying if Trump isn’t willing to behave in a more disciplined fashion, then Lewandowski’s departure may do little good. “I don’t know if it helps Trump personally unless he is willing to completely change through the Manafort model,” the adviser added. Power struggle This marks the latest fallout in the power struggle between Lewandowski and Manafort – ultimately seen as a major victory for Manafort that could allow him to run the campaign in a more traditional sense. Some sources within the campaign are expecting Manafort and his deputy, Rick Gates, to fill the power void that Lewandowski leaves behind. The Trump campaign has started hiring what one source called “middle level staffers with political experience” in key battle ground states across the country, scheduled to start after the July convention. Despite the Trump campaign’s efforts to create a more well-oiled machine, they are still not operating at full capacity due to internal feuding. RELATED: Anti-Trump delegate faction says it’s raising cash, faces long odds “No one is really sure who is running things. It’s very disorganized,” said one GOP source working with the campaign. Most of the new hires have not begun their actual jobs yet, but are still in the process of filling out the enormous amount of paperwork – including disclosures and noncompetes that come with being employed by Trump, said one source. There are particular frustrations that the campaign has yet to hire a traditional communications team that can handle the high volume of media requests that comes with being a nominee for president, according to two sources in and around the campaign. Currently, the team consists of only Hope Hicks, Trump’s spokeswoman. “No one is managing the message,” one source close to the campaign told CNN. Last month, the campaign hired long-time consultant and operative Jim Murphy as political director, replacing Rick Wiley after clashes with Lewandowski and other original Trump hires led to Wiley’s abrupt departure from the campaign. One of the top priorities with Murphy in place was building out the campaign’s communications team, this person told CNN. In what was widely viewed as an incredible demonstration of the deep animosity towards Lewandowski from some factions of the campaign, one Trump adviser, Michael Caputo, tweeted this on Monday minutes after the news broke about Lewandowski: “Ding dong the witch is dead!” Caputo later expressed “regret” for issuing the tweet and resigned his position as director of communications for caucus operations at the 2016 Republican convention.