McCain secured his party's nomination this month after primary victories in Texas and Ohio, followed the next day by an endorsement from the president. Bush and McCain haven't been seen together since, but that doesn't mean the relationship has gone sour.
The president is helping his one-time rival, and many other Republicans, by continuing a torrid fundraising pace that has marked his time in office.
So far this year, Bush has been the headliner at 15 fundraisers for the Republican National Committee, candidates for federal and state office and other groups, generating more than $28 million.
During a single day in Florida about two weeks ago, Bush raised $1.4 million for the RNC at a pair of events while officially traveling to talk about trade.
"We appreciate the time and effort the president spends ensuring Republicans up and down the ticket have the necessary resources," said RNC spokesman Alex Conant.
One of the main themes of the 2008 election is the excitement generated by Democratic candidates, as reflected in copious donations given to them.
Obama has taken in $193.6 million so far, according to the Federal Election Commission, eclipsing Clinton's $169 million. McCain trails with $65.6 million.
Those numbers tell only part of the story, however.
With Bush leading the way, the RNC has taken in $108 million during this election cycle, and had $25 million available cash at the end of February, records show. The comparable figures for the Democratic National Committee: $62 million raised, with $4.8 million unspent.
While those aren't Obama-esque numbers, it's money on the Republican side that will certainly be put to good use in the weeks and months ahead.
At the same time, the Democratic candidates will be doing more spending than saving, buying television advertisements in Pennsylvania, North Carolina and Indiana and traveling extensively.
The White House regularly schedules presidential fundraisers to dovetail with out-of-town speeches and events. Last Thursday, for example, Bush took Air Force One to Dayton, Ohio to deliver a speech on the Iraq war and the fight against terrorism. Rather than return directly to Washington, he made stops in Bellbrook, Ohio and Sewickley, Pa. to raise money for the respective states' Republican committees at events in private homes.
The president's fundraising visits are coordinated by the White House Office of Political Affairs, a team of advisers who know that money raised for swing states such as Pennsylvania and Ohio could reap big rewards later this year.
"It's appropriate, and it is acknowledging that the president, as head of the party, has a role to play at these events," said Scott M. Stanzel, a deputy White House press secretary.
Under federal election law, the White House calculates the amount of time the president spends on political events during such trips and charges the candidate or committee a pro-rated portion of travel expenses. The cost of Secret Service protection and the time of staff who may have accompanied the president for his official events are not included, Stanzel said.
The president has appeared at 306 fund-raising events since taking office, including those for his own re-election, raising a staggering $760 million, according to records maintained by Mark Knoller of CBS News.
Such figures illustrate that Bush remains popular with a loyal segment of the Republican base, even as his approval ratings hover in the low 30s.
"The president has the power of incumbency and has always had huge fundraising prowess," said John M. Kane, a former chairman of the Maryland Republican Party. "He can dwarf the efforts of many, including those with the so-called momentum."
Both Bush and McCain have tacitly acknowledged that the president's primary advantage in helping a Republican succeed him in the White House is as a cash-collector, not a hustings campaigner.
"If he wants me to show up I will. If he wants me to say, 'You know, I'm not for him,' I will," Bush said during his endorsement of McCain.
"I'll be pleased to have him with me both from raising money and the much needed finances for the campaign, and addressing the challenging issues that face this country," the senator said, adding that Bush had a "busy schedule" that might keep him off the campaign trail.
Bush's aggressive fundraising provides fodder for partisan critics who want to link McCain and other Republican candidates to an unpopular president.
"They can't take his money and then distance themselves from his legacy of failure," said Brad Woodhouse, president of Americans United for Change, a liberal group working to elect Democrats.
"On the biggest issues facing America today - the war in Iraq and the economy - the vast, vast majority of Republicans have supported Bush, they helped create his legacy and there is no way we are going to allow them to take his campaign cash and then try to distance themselves from him," Woodhouse said. "That dog won't hunt."
But such arguments don't worry Republican donors and candidates who are well aware of the power of money. "Any candidate," said Kane, the former Maryland chairman, "would appreciate the help of a huge fundraising powerhouse like the president's."