Senator Barack Obama, inching closer to the Democratic nomination, seized on the occasion while speaking about the mortgage crisis in Nevada.

ÒJohn McCain is having a different kind of meeting,Ó Mr. Obama said after meeting a family in Las Vegas on the verge of losing its house to foreclosure. ÒHeÕs holding a fund-raiser with George Bush behind closed doors in Arizona. No cameras, no reporters. And we all know why.

ÒSenator McCain doesnÕt want to be seen, hat in hand, with the president whose failed policies he promises to continue for another four years.Ó

The politicking seemed far removed from the sunny day at the White House in March when Mr. McCain, still flush from his triumph over a crowded primary field, and Mr. Bush appeared like two old friends. Despite a bitterness attached to the 2000 primaries, Mr. McCain promised Òto have as much possible campaigning events together.Ó

More than once, though, he alluded to Mr. BushÕs ÒheavyÓ or ÒbusyÓ schedule, which in hindsight perhaps had more significance than it might have seemed.

Mr. Bush made an early fund-raising stop in New Mexico on Tuesday, but his Òheavy scheduleÓ otherwise included a visit to Silverado Cable, a company in Mesa, Ariz., that makes electrical wiring for aircraft.

He did not mention Mr. McCain, nor did Mr. McCain mention him in Denver.

For Mr. Bush, with seemingly irreversible public disapproval in the polls, the start of his campaign to help elect a Republican successor could hardly have seemed more humbling, though the White House maintained its typical enthusiasm and optimism.

ÒHeÕs not bothered in the slightest,Ó the White House press secretary, Dana M. Perino, said. ÒHe fully understands how campaigns for presidents work, and heÕs comfortable in his own skin.Ó

Bruce Bartlett, a conservative economist who wrote ÒImpostor: How George W. Bush Bankrupted America and Betrayed the Reagan Legacy,Ó said core supporters possessed a hardened realism about Mr. McCainÕs prospects, understanding the challenges but not yielding to them.

ÒEven diehard Bush supporters know heÕs an albatross around the neck of the nominee,Ó Mr. Bartlett said in an interview.

At the same time, he noted the presidentÕs fund-raising prowess. Despite the efforts by the McCain camp to keep at armÕs length a president with an approval rating stalled at 28 percent, it is worth remembering that that 28 percent can be fiercely loyal and often wealthy.