For that reason and more, other Republicans are all but counting him out.

"This is about as close to terminal as you can get without actually dying," said Alex Vogel, a GOP strategist and one-time aide to former Senate Majority Leader Bill Frist, R-Tenn. "In medical terms they would say his campaign is in grave condition. The last rites are being uttered."

But one of his top rivals said it was premature. "I'd be the last one to think John McCain is done," Rudy Giuliani said during a campaign stop in New Hampshire.

The departures of Nelson, a veteran of Bush's successful 2004 re-election effort, and Weaver, a longtime aide who played a key role in McCain's failed 2000 bid, were the culmination of a monthslong power struggle between two factions of senior McCain advisers over the course of his second presidential bid.

McCain's campaign said Mark Salter, a top aide whom some consider the senator's alter ego, will continue to advise him and the campaign without pay, an arrangement worked out last week. But two officials said Salter's adviser role will be limited to McCain's official Senate duties.

Other senior aides followed Nelson and Weaver in resigning Tuesday, including deputy campaign manager Reed Galen, political director Rob Jesmer and finance director Mary Kate Johnson.

Several officials, who spoke on the condition of anonymity to discuss private conversations, said McCain sought the leadership change at the campaign's highest rungs because he believed Nelson and Weaver had mismanaged his bid. But other officials close to the two disputed any notion that they were fired.

The two announced their resignations in short statements Tuesday. They said it was an honor to serve McCain, and both praised him as the best Republican to be the party's nominee and win the White House.

Lackluster fund-raising and a high rate of spending left McCain's campaign with just $2 million on hand six months into the year, forcing him to lay off dozens of campaign aides last week across all areas of the organization.

At the time, Nelson and Weaver acknowledged that the campaign incorrectly assumed that it would raise more than $100 million this year, and built an expansive national campaign organization based on that assumption.

McCain's own embrace of politically disastrous positions also contributed to his woes.

He staunchly backed both Bush's troop increase for the Iraq war, an unpopular conflict with the public but one supported by most Republicans, and the president's legislation to grant eventual citizenship to millions of illegal immigrations — a measure that has divided the GOP.

Over the past six months, McCain found his donors and supporters turned off by what they viewed as the senator supporting the policies of a lame-duck president with abysmal approval ratings. That caused McCain's fund-raising and polling to suffer.

He raised just $25 million in the first half of the year, coming in third behind Mitt Romney and Giuliani for two consecutive financial quarters.

McCain's support in national polls has slipped, and he is in single digits in some surveys in Iowa and South Carolina, trailing Giuliani, the former New York mayor; Romney, the ex-governor of Massachusetts, and Fred Thompson, the actor and former Tennessee senator who hasn't officially entered the race.