Donald TrumpDonald John TrumpLawmakers prep ahead of impeachment hearing Democrats gear up for high-stakes Judiciary hearing Warren says she made almost M from legal work over past three decades MORE Jr. says his father's firing of campaign manager Corey Lewandowski will help the billionaire move into the general election fight against Hillary ClintonHillary Diane Rodham ClintonWill the Horowitz report split the baby? Gabbard commemorates John Lennon's passing by singing 'Imagine' Bannon: Clinton waiting to enter 2020 race and 'save the Democratic Party from Michael Bloomberg' MORE.

“Listen, I think it’s just, you know, the nature of moving on,” Trump Jr. said Monday on MSNBC. "I think there’s things that, you know, Corey was incredible at.

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“But again, I think now, you walk into a bigger machine and you’re going up against the Clinton machine, which is very big and has the media behind it and has everyone behind it, as opposed to sort of America’s real message. I mean, I think it has to change and I think we have to, you know, evolve towards that.”

Trump Jr. said Lewandowski’s ouster will help his father’s team refocus before next month’s Republican National Convention.

“I think it’s just the timing,” he said. "We’re not going to delay everything until the convention and then come out of that, but I think we’re going to do that, regroup, get everything set and we’re going to come out of the convention running.

“We’re always going to be a lean, mean machine. So we’re always going to run that way as that’s the way my father thinks government should run. So we’re going to run mean and lean, but we do also have to evolve.”

Trump Jr. added that his father’s campaign wants a closer relationship with the Republican National Committee (RNC).

“Well, I think that’s certainly going to change,” he said of strain between his father’s team and the RNC.

"And, I mean, as you know, this is a busy, busy place and everyone is going and everyone is all the time on. So I think there could have been some miscommunications throughout that process. So I think this will simplify some of that.”

Donald Trump, the Republican's presumptive nominee for president, on Monday fired Lewandowski amid reports of tensions roiling within the businessman’s campaign. Lewandowski reportedly clashed with campaign chairman Paul Manafort amid rising concerns that the team is unprepared for the battle against Clinton, his Democratic counterpart.

“I think I’m a very intense person and my expectation is perfection, because I think that’s what Mr. Trump deserves,” Lewandowski said on CNN.