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McCain said Tuesday his bid for the White House is 'going well.'

WASHINGTON (CNN) - Sen. John McCain described his campaign for the White House as "going well" and vowed Tuesday to continue his bid for the GOP presidential nomination even as several of his senior staffers said they were leaving the campaign.

Campaign Manager Terry Nelson and Chief Strategist John Weaver announced earlier in the day they were resigning from their posts. Within a few hours, CNN confirmed that Deputy Campaign Manager Reed Galen and Political Director Rob Jesmer were also leaving the campaign.

McCain is already under fire from conservatives for his position on immigration as well as Independents for supporting the Iraq war. His bid for the White House took a hit last week when it reported only having $2 million in the bank after raising more than $11 million in the second quarter. Major campaign layoffs followed and the resignations Tuesday of several senior staffers further fueled speculation that McCain would drop out of the race.

But after delivering a speech on Iraq from the Senate floor, McCain sought to silence any suggestions that he was throwing in the towel.

"Of course," McCain responded to a reporter who asked if would continue to campaign for the presidency. "With the same people who were running it before. We were a collective team and I'm very grateful for their contributions that they will continue to make."

Rick Davis, another McCain political advisor, will take over as campaign manager. In a statement released by the campaign Tuesday, Davis echoed McCain's comments that the campaign was moving forward.

"This campaign has always been about John McCain and his vision for reducing federal spending, defending traditional values, and winning the war against Islamic extremists. Today we are moving forward with John's optimistic vision for our country's future."

But McCain, known for being a "straight talker" refused to discuss the departure of several members of his senior campaign team.

"These are very good and close friends of mine," McCain told the reporters. "I am grateful for their friendship, which will continue in the future as it has been in the past."

Nelson and Weaver, themselves, had been criticized for poorly managing the campaign's financial resources and both acknowledged last week that they miscalculated by thinking he would raise $100 million in 2007. But in the first six months of this year, McCain has raised a little more than $24 million.

It was not a surprise when Nelson and Weaver told reporters last week the campaign would undergo a major restructuring that included the layoffs and a new focus primarily on the early voting states of Iowa, New Hampshire, Nevada and South Carolina. It had been widely speculated that Nelson might eventually leave the campaign, but not Weaver - a long time aide and confidante to the Arizona senator.

Sen. Lindsey Graham, a close McCain ally, said that the campaigns infrastructure needed to be changed.

"Shaking up John's campaign is probably something that's smart, because we spent too much money with too little to show for it," said Graham, a South Carolina Republican. "And if you don't adjust in the politics of war you can pay the price."

But why Weaver, who has spent the past seven years preparing McCain for another presidential bid? When McCain returned from Iraq he met with Nelson and Weaver to look at the fundraising numbers and the staff reorganization. A campaign advisor, who spoke on the condition of anonymity, said they could "not satisfy" McCain "that they had a good plan" and the Arizona senator was also angry over the amount of money the campaign was burning through. After conversations with McCain, both Nelson and Weaver walked away feeling they had lost the senator's confidence and their "Plan B approach wasn't satisfactory to him."

An official in the McCain campaign, who also spoke freely on the condition of anonymity, said the senator had decided Davis would take a bigger role in the campaign, which Nelson and Weaver opposed. So McCain told his aides "do what you want" but Davis is back in a lead role. Davis had been privately advocating a much different strategy for McCain. Nelson and Weaver resigned.

Another source involved in the McCain campaign's internal deliberations said the senator's wife, Cindy, and Sen. Trent Lott, R-Mississippi, both pushed for change after seeing the disappointing fundraising numbers

"Cindy is the main catalyst for change," said the source, who added that Lott "has John's ear and says he has to find a way to shake things up and get a fresh look."

Perhaps even more shocking to Washington insiders is Mark Salter's decision to take a reduced, voluntary role in the campaign. Salter is McCain's long-time chief-of-staff who Salon.com once described as "The Voice of Sen. John McCain." Salter co-wrote several books for McCain including: "Faith of My Fathers: A Family Memoir."

Salter will retain his title as senior advisor to McCain assisting with communications strategy and speechwriting, but it will be in an unpaid capacity and no longer have day-to-day responsibilities.

While Davis, who was part of McCain’s 2000 bid for the White House, will take over as campaign manager a search is now underway to promote someone who is "politically savvy" enough to take on the details that were once handled by Nelson, said a campaign source.

"I think what you've got is people's strengths are coming out," said Graham. "John Weaver is a great tactician. Mark Salter is one of the best wordsmiths I've ever met. Rick Davis' skills are in the management area. It's getting the right people with the right skill base. There's nothing wrong with the people. I don't think they had the right skill sets."

The plan is now to continue to focus on Iowa, New Hampshire and South Carolina. Sources within the campaign said they are confident that the infrastructure they built in all of these states will withstand the campaign's current woes.

Still, one former McCain campaign aide surveyed Tuesday's fallout and said the departure of Weaver sends the signal that "everything done up until now was wrong."

And Stuart Rothenberg, a well respected non-partisan political analyst, said that McCain now has a difficult task of resuscitating his campaign.

"I think clearly McCain has fallen out of the top tier of the Republican race and it is unclear how long the campaign can survive," said Rothenberg, editor of the Rothenberg Political Report. "I think it is very unclear whether they are going to have the resources to continue in all of the early states or rather hunker down in New Hampshire or Iowa and take a stand. This is a campaign that needs to turn around public psychology sometime over the next few months or they are not going to be able to raise any money and will be kicked to the curb by most people."

– CNN's Ted Barrett, Dana Bash, Candy Crowley, Sasha Johnson, Ed Henry, John King and Mark Preston contributed reporting for this story -