The McCain campaign just sent out the following bombshell via email:

ARLINGTON, VA - Terry Nelson, Campaign Manager and John Weaver, Chief Strategist for John McCain 2008 issued the following statements:

"This morning I informed Senator McCain that I would be resigning from his presidential campaign, effective immediately. It has been a tremendous honor to serve Senator McCain and work on his campaign. I believe John McCain is the most experienced and prepared candidate to represent the Republican Party and defeat the Democratic nominee next year." - Terry Nelson, Campaign Manager

"As of today, I have resigned my position as chief strategist to John McCain's presidential campaign. It has been my honor and a distinct privilege to serve someone who has always put our country first. I believe that most Americans will come to the conclusion that I have long known there is only one person equipped to serve as our nation's chief executive and deal with the challenges we face, and that person is John McCain." - John Weaver, Chief Strategist

MORE: From the Associated Press:

One official said Terry Nelson resigned as campaign manager for the Republican presidential candidate and John Weaver stepped down from his post of chief strategist on Tuesday. But other officials said Nelson was fired.

The officials spoke on the condition of anonymity because the shake-up has not been made public.

Two officials said Rick Davis, a longtime aide to McCain, will take over the campaign.

MORE: The mystery deepens with this tidbit from Marc Ambinder:

Republicans close to the campaign say that Mark Salter, McCain's long-time chief of staff and co-author of his five books, is also leaving the campaign.

The sources said that the three did not split from McCain amicably.

The outlines of a complete blowup are emerging. Nelson's departure might be understandable, given that he was a Bushie brought in after '04. But Salter has been with McCain from the very beginning, and Weaver has been one of McCain's most trusted advisor's since joining his 2000 campaign. Needless to say, the departure of the three, especially under such abrupt and mysterious circumstances, does not bode well for the McCain campaign.

MORE: McCain has just released the following statement:

"Today, John Weaver and Terry Nelson offered their resignations from my presidential campaign, which I accepted with regret and deep gratitude for their dedication, hard work and friendship. Terry is a consummate professional, who has ably lead this campaign through a challenging political environment. John Weaver has been my friend and trusted counselor for many years and to whom I am greatly indebted. In the days and weeks ahead this campaign will move forward, and I will continue to address the issues of greatest concern to the American people, laying out my vision for a secure and prosperous America."

MORE: Jonathan Martin adds a bit more context:

McCain fired his campaign manager this morning, prompting his longtime chief strategist to resign. Soon after, McCain's chief of staff of 18 years followed the two out the door.

Terry Nelson, an Iowan who had been a top operative in the Bush-Cheney re-election campaign, was forced out, reportedly at the urging of Davis. With Nelson gone, John Weaver, McCain's closest political adviser going back to the 2000 campaign and a sometimes Davis rival, tendered his resignation. Weaver's move then spurred Mark Salter, perhaps the closest personally of any staffer to McCain and the co-author of all his books, to also resign his post as campaign COO.

As one McCain source put it, "It's Rick Davis's show now."