The calls come at least once a week these days, with growing urgency: friends of the Republican presidential candidates, aides to the candidates, and often the candidates themselves, wondering if Al Hoffman Jr. might be ready to lend a hand.

“How are you doing? What are you feeling? What are you thinking?” Mr. Hoffman, a Florida real estate developer who was a co-chairman of George W. Bush’s presidential campaigns, said in describing the calls. But Mr. Hoffman, one of the Republican Party’s most sought-after fund-raisers, remains unconvinced that he should tap into his extensive network of contacts to raise money for any of them.

“None of the candidates have instantly identified themselves as a leader for the Republican movement,” Mr. Hoffman said. “The Bush family were instantly identifiable as leaders.”

He is far from alone. Two and a half years after Mr. Bush left the White House, the formidable network of Republican donors he assembled has largely melted away. Fewer than one in five of Mr. Bush’s Rangers and Pioneers, the elite corps of “bundlers” who helped Mr. Bush smash fund-raising records in his two runs for the White House and remain the gold standard of Republican fund-raising, have contributed to any of the current Republican candidates, according to a New York Times analysis.