Republican presidential candidate Jeb Bush is slashing his campaign budget with across-the-board pay cuts and other changes, overhauling an operation that started as a political juggernaut but now may need to stay lean to survive. 

The one-time GOP front-runner has seen his political momentum undercut by outsider candidates Donald Trump and Ben Carson, who now lead in most polls, relegating the former Florida governor to the middle of the pack. 

In a bid to recalibrate its strategy and operations, the Bush campaign plans to cut its budget by as much as 45 percent. This includes pay cuts of 40 percent, cuts to travel costs and a downsizing of its Miami headquarters staff, Fox News has learned. 

The overall changes will save the campaign approximately $1 million a month, Bush senior sources say. In recent months, Bush's biggest expenses have been air travel and staff, having spent $1.6 million on payroll alone over three months. 

An internal campaign memo on the changes, obtained by Fox News, acknowledged the shifting dynamics in the race. 

"It's no secret that the contours of this race have changed from what was anticipated at the start. We would be less than forthcoming if we said we predicted in June that a reality television star supporting Canadian-style single-payer health care and partial-birth abortion would be leading the GOP Primary," the memo said. 

The changes come despite a combined fundraising haul of well over $100 million by his campaign and a pro-Bush super PAC. In another setback for Bush, fellow Florida politician Sen. Marco Rubio has been gaining in the polls, often edging out Bush -- increasing frustration not only among some of Bush's network of donors, but also longtime Florida supporters. 

The campaign is describing the budget changes as an effort to focus on what matters most: Increasing his presence in the early-voting states, with an eye toward laying out a modified path to winning the nomination. 

"We are making changes today to ensure Jeb is best positioned to win the nomination and general election. Jeb is the one candidate with a proven conservative record, bold ideas and the strong leadership needed to fix the problems America faces," campaign spokeswoman Kristy Campbell said in a statement. "We moving our resources into the states to ensure that voters in primary and caucus states are introduced to his record and vision for the future." 

In the internal memo, the Bush campaign also touted its extensive field operations in the early voting states of Iowa, New Hampshire and South Carolina, as well as its formidable fundraising effort that has raised roughly $25 million so far this year -- not counting the over $100 million raised by the pro-Bush super PAC, Right to Rise USA, that is separate from the campaign. 

In the coming days, the campaign hopes to regain lost ground, and strengthen its overall message by concentrating on Bush's record as Florida governor where he cut state budgets and issued tax cuts. The mantra, according to the campaign, will be that "Jeb Can Fix It." 

"We're going to focus the argument of this campaign around the fact that after seven years of incompetence, corruption and gridlock in Washington, we need a president 'Who Can Fix It.'" The memo states. "Jeb is the only person in the field on both sides of the aisle who can make this statement." 

The full e-book on Bush's tenure in Tallahassee will also be released in the "next couple weeks," according to the internal memo.