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Having done no fundraising, zero advertising, and little traditional organizing for the bulk of his presidential campaign, Donald Trump is finally starting to act more like a conventional candidate, at least when it comes to asking for money.

Trump and the Republican National Committee this week announced that 80 additional GOP bundlers have signed on to their joint fundraising effort, essentially quintupling the number of people helping round up money for Trump and his party. In May, the billionaire businessman held his first official fundraiser with the RNC. In June, he announced with much fanfare his first emailed fundraising solicitation.

Trump's belated pivot to fundraising has raised questions over how he will reconcile his quest for checks with his earlier claim that he's blissfully independent of big donors. In September, Trump boasted on Twitter: "By self-funding my campaign, I am not controlled by my donors, special interests or lobbyists. I am working only for the people of the U.S.!"

But the bigger question now facing Trump is whether, having waited till the last few months of the contest to ask supporters for money, he can possibly raise enough to run even a barebones campaign. In the last presidential election, Barack Obama spent $721 million and GOP nominee Mitt Romney spent just under $450 million. Add in political party and outside group spending, and teams Obama and Romney each spent a little over $1 billion apiece.

The RNC has raised a healthy $150 million so far, well ahead of the DNC-but that's still far short of the hundreds of millions it typically takes to run a national campaign. Trump himself had only raised about $18.8 million as of the end of May, having loaned himself $45.7 million of his $64.6 million in receipts. As has been widely reported, Trump's latest public disclosures showed only $1.3 million cash on hand, compared with Hillary Clinton's $42.5 million.

Trump has shrugged off the disparity, suggesting that he could self-finance his general election campaign if need be-though it's unclear whether he would follow through. Trump did win the GOP primary despite more than $40 million spent to defeat him, and his unconventional campaign may still hold surprises. By one estimate, Trump has earned $3.8 billion in unpaid media exposure, compared with $1.7 billion in free media for Clinton.

But there's a world of difference between a primary contest, particularly one that featured 17 GOP contestants, and a general election, say political experts. The heart of a general election campaign is voter mobilization, says Lara Brown, an associate professor at George Washington University's graduate school of political management. That means identifying, registering, and turning out millions of voters, using sophisticated, data-driven voter identification and targeting tools that Democrats have, in recent elections, leveraged more successfully than Republicans.

"You have a campaign that has been largely operating by the seat of its pants-hasn't had to do systematic fundraising, hasn't done methodical grassroots outreach and mobilization, and has been relying on free media, not paid media, to foster name recognition and ID," says Brown. Trump's earned media advantage is also likely to evaporate in the general election, Brown adds, since media coverage is now likely to focus more equally on the two remaining candidates.

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Free media "does compensate to some degree," says Darrell West, director of governance studies at the Brookings Institution. "But the problem is that when the free media coverage turns negative, he doesn't have his own resources to defend himself." Free media also won't help Trump defend himself against attack ads. Notes West: "In the general election, we know that the criticism will be sustained and well-funded. So that will be a new challenge for him."

Trump is backed by a motley array of super PACs, but they've collected only about $4 million between them. Ken McKay, the head of a leading pro-Trump super PAC dubbed Rebuilding America Now, has predicted that his group will be spending at the same rate as the leading pro-Clinton super PAC by October. But Trump has yet to single out and give his blessing to any one PAC. By contrast, that leading super PAC backing Clinton, Priorities USA Action, which has her unofficial sanction, had raised $88 million and had $52 million cash on hand as of May 31.

Trump's nascent fundraising, moreover, has been marred by repeated stumbles.

A full 60 percent of the emails from Trump's first solicitation reportedly landed in spam. The Trump team's estimates of $3.3 million in receipts from a single email blast have been criticized as wildly inflated. Trump's political expenditures have also come under fire for directing large sums both to his own companies, and to vendors cozy with his campaign staff.

Trump has tangled with the business leaders and K Street lobbyists who typically form the backbone of GOP fundraising operations. His attacks on international trade deals have drawn rebukes from the U.S. Chamber of Commerce. His attacks on lobbyists and special interests have convinced many to skip next months' GOP convention in Cleveland, and driven off many potential GOP bundlers. Corporate donors, too, have cut back on their convention funding.

Billionaire industrialists Charles and David Koch, who at one time had pledged to spend close to $900 million on the election, will reportedly focus on House and Senate races this time.

The upshot is that instead of spearheading a coordinated campaign that helps raise money for candidates all the way down the ballot-the typical role of a presidential nominee-Trump will rely heavily on the RNC to do his campaign organizing for him. Already at pains to unify a party deeply divided over Trump, the RNC has formed a joint fundraising committee with him. But the committee launched only in May, and has yet to report any receipts. By contrast, Clinton's joint fundraising operation with the DNC, the Hillary Victory Fund, has raised $60.6 million.

Will it matter? Perhaps not. This election could still be scrambled by any number of wild cards-a domestic terror attack, a fiscal crisis, a Zika outbreak. But Trump has barely more than 100 fundraising days remaining between now and Election Day. That's precious little time to amass a presidential war chest and build the infrastructure to turn out some 60 million voters. Trump's controversial campaign faces many challenges. At the top of the list would be money-were that spot not occupied by Trump himself.