President Bush has headlined a fund-raising event to help John McCain finance his campaign to succeed him, but most of the big-money backers who helped reelect Bush in 2004 haven't pulled out their checkbooks for McCain - or asked their friends to chip in either.

Of the 548 leaders of Bush's vaunted money-raising machine, about 43 percent have contributed to McCain, a Globe review of finance reports covering the period through May 31 shows. Even fewer of them solicited and bundled donations from others for McCain, as they did for Bush four years ago.

About 25 percent of the elite Bush money team gave to another Republican or, in several cases, to a Democrat, but not to McCain. Nearly a third remained on the sidelines, not contributing to any presidential candidate.

McCain's struggle to mobilize the Bush fund-raisers is in part a sign of the disaffection among some GOP stalwarts for McCain, who positions himself as a party rebel on some issues. But it's also a sign of the obstacles that any Republican nominee would face in exciting elite GOP donors at a time of discouraging poll numbers driven by economic turmoil and frustration over the Iraq war.

The McCain campaign is trying to make a virtue out of its modest success in recruiting the Bush fund-raisers. In response to the Globe's analysis, McCain spokesman Brian Rogers said: "It appears you've proved that John McCain isn't Bush's third term after all," referring to a characterization the Obama campaign has made and McCain has rejected.

Bush's major fund-raisers were dubbed Rangers if they raised more than $200,000 in 2004, or Pioneers if they brought in more than $100,000.

In heavily Democratic Massachusetts, some Bush fund-raisers remain loyal to one of McCain's chief GOP rivals, Mitt Romney, the favorite son and former governor who suspended his candidacy in February.

"I would probably support John McCain if he chooses Mitt Romney as his running mate; other than that, I will not support John McCain," said venture capital fund manager and Staples founder Thomas G. Stemberg, a Bush pioneer who raised large amounts for Romney but also contributed the individual maximum, $2,300, to Senator Barack Obama in March 2007.

Concessions magnate Joseph J. O'Donnell of the Boston Culinary Group was a Bush Ranger who raised substantial sums in this race for his fellow Belmont resident, Romney. A registered independent who often contributes to Democrats, O'Donnell donated $1,000 to McCain in late March, after Romney dropped out, and said he will support McCain over the less experienced Obama, but has not raised funds on McCain's behalf. Like Stemberg, O'Donnell said he hopes McCain "is smart enough to choose Mitt" as his running mate.

Bush Pioneer Kenneth J. Kies, managing director of a Washington-based tax consulting and lobbying firm, was a late giver to McCain, donating the maximum in May. Kies said his contribution was unsolicited after he sat out the nominating contest, which he termed "a scrum."