As Barack Obama embarks on the first privately funded general election campaign since Watergate, his latest cash-flow numbers suggest he'll want to soon win over Hillary Clinton's donors to keep his fundraising edge -- and make his reversal on public financing worth his while.

The presumptive Democratic nominee plans to meet with Clinton and her top fundraisers Thursday in Washington.

The session presents an opportunity to shore up his reserves, after he reported his weakest fundraising of the year, pulling in $22 million in May.

That figure is nothing to sneeze at, but for the first time this year GOP rival John McCain practically matched him, pulling in $21 million. Considering his cash on hand, McCain is virtually on the same financial footing as his Democratic rival.

Obama's decision Thursday to forgo $84 million in public financing suggests the Illinois senator expects to haul in much better numbers in the months ahead.

As he sets up a meeting with Clinton donors, the two Democrats seem to be in a unique position to help each other.

The former first lady, who bowed out of the Democratic contest on June 7, reported $22.5 million in campaign debt at the end of May, more than half of which was a personal loan to her presidential campaign.

The Obama camp has not yet devised a plan to help Clinton pay off that debt, but her backers are eager for some aid, saying such a gesture could help Obama, in turn, win over her still-frustrated supporters.

"It's far more productive for Obama to have Hillary 100 percent focused and engaged on campaigning and raising money for him in the fall rather than having to do fundraisers at the same time to retire her debt," said Hassan Nemazee, a Clinton national finance chairman.

"It would clearly make life easier for those of us in the Clinton world who would like to help Senator Obama raise the types of monies that are necessary from the Clinton world to be in a position to point out, 'Look what Senator Obama has done for Senator Clinton."'

The two former rivals plan to campaign together for the first time Friday, a sign that they will in fact join forces -- and convince supporters to do the same.

And despite his latest numbers, Obama is still the fundraising giant of the 2008 campaign.

Since the presidential campaigns began last year, Obama has raised $287 million, Clinton has raised $209 million and McCain has raised $115 million.

He's expected to keep his cash advantage over McCain, who with his decision to take the public financing will be limited to $84 million for the November election.

"You're talking about an enormous strategic and tactical advantage for the Obama campaign," said Chris Kofinis, former spokesman for Democratic candidate John Edwards. "He could literally be the first 200-, 300 million-dollar candidate post-convention, giving him unlimited resources to compete, not only in every battleground but in red states across the country."

But Obama is under such stiff criticism for abandoning his earlier pledge to take the public financing that if he doesn't blow McCain away in fall fundraising, the turnabout will be undoubtedly seen as a losing gambit.

Editorials across the country blasted Obama for the decision Friday. The Washington Post wrote, "his effort to cloak his broken promise in the smug mantle of selfless dedication to the public good is a little hard to take."

"He has sort of ceded this rhetorical and ethical high ground that he could have as a reform candidate," said Kevin Madden, former spokesman for GOP candidate Mitt Romney, who ran against McCain in the primary. "(McCain) has an advantage here he can exploit."

Kofinis said public financing does not rate as a major issue among voters. And Obama has said he made the decision to opt out because he expects McCain to have significant help from the Republican Party and outside groups.

Meanwhile, a new Newsweek poll showed Obama with an incredible national advantage over McCain.

Though most polls since Obama clinched the nomination show him leading by about 5 percentage points, Newsweek's survey gave him a 15-point lead.

The poll, taken Wednesday and Thursday of 896 registered voters, showed Obama leading 51-to-36 percent. The poll had a margin of error of 4 points.

It also showed him polling at 69 percent among Clinton supporters. Eighteen percent of them said they were supporting McCain, while 13 percent were undecided.

For those Clinton supporters staying on the sidelines, McCain has taken special care to court them. He held a virtual town hall meeting with them last weekend and has set up a new group to court Democratic voters.

Despite his fundraising disadvantage, national Republicans have provided him an ample buffer.

The Republican National Committee ended June with 13 times more money in the bank than the Democratic National Committee. The RNC had $53 million cash on hand to the DNC's $4 million. Both parties are allowed to assist their presidential candidates with coordinated campaigns.

The Associated Press contributed to this report.