If there's one thing Donald Trump has staked his personal brand and presidential campaign on, it's that he's really good at making money. But his latest campaign finance filings tell a somewhat different story.

The presumptive Republican nominee had just $1.3 million in cash on hand at the end of May, according to FEC filings published Monday. Hillary Clinton, his presumptive Democratic challenger, reported having $42 million on hand last month. Bernie Sanders, who has all but conceded the nomination to Clinton, had $9.2 million on hand. And perhaps most damning of all, Trump had less money than the campaigns of Ted Cruz and Ben Carson, both of whom had dropped out of the race in previous months.

A war chest of just over $1 million is about what would be expected of a small congressional campaign in an off-year election; indeed, 121 members of Congress currently have more money than Trump. Clinton's campaign staff currently numbers about 700 people. The Trump campaign has just 70 employees on its payroll.

Trump's modest war chest is another sign of a faltering campaign increasingly affected by disorganization and infighting in the critical months before the general election. The same day the FEC filings were released, Trump fired his campaign manager and right-hand man, Corey Lewandowski, in an unusual last-minute reshuffling effort.

Trump, ever the optimist, brushed off the dismal fundraising numbers in a statement Tuesday.

"If need be, there could be unlimited 'cash on hand' as I would put up my own money, as I have already done through the primaries, spending over $50 million dollars," Trump said. "Our campaign is leaner and more efficient, like our government should be."

Trump often boasts that he doesn't need donors or special interests to help fund his campaign, but that tune may change if he wants to make payroll next month. He raised just $3.1 million in May, the same month he clinched the Republican nomination; he spent $2.2 million of his own money to cover a spending gap.

Yet Trump doesn't seem bothered by those numbers. "To date, the campaign's fundraising has been incredible and we continue to see a tremendous outpouring of support for Mr. Trump and money to the Republican Party," his statement continued.

Republican donors say they hope to raise $500 million for Trump before election day, according to the New York Times. This would require Trump to cooperate with the Republican National Committee (RNC) on joint fundraising efforts.

Presidential nominees typically work closely with their national parties to raise money for competitive down-ballot races throughout the country in addition to the presidential election. Trump, however, is doing things differently. He is relying on the RNC to do the groundwork of campaigning for him in swing states, yet has not shown much enthusiasm for fundraising aggressively on their behalf. The RNC had $20 million in May, a fraction of the $60 million they had the same month in 2012 when Mitt Romney was the nominee.

It's not a surprise that donors are failing to write big checks for Trump, since he has spent much of the past year blasting them as corrupt special interests and insisting that he can self-fund all the way to the White House. It may now be too late for Trump to reverse tack and begin wooing Republican donors without any real fundraising infrastructure.

Meanwhile, Clinton is having no problem raking in cash from Democratic donors. On Monday, she attended a celebrity-packed fundraiser in New York that cost a reported $33,000 per plate.

Trump's FEC filings illuminate some of the questionable ways that his campaign is spending the few dollars it has. He has not spent anything on advertisements in the last month, nor has he devoted any resources to campaigning in battleground states. The Clinton campaign, meanwhile, has spent $21 million on television ads hammering Trump in crucial swing states across the country.

According to the filings, Trump's most significant expenditures were on things directly related to himself, his family, or his own businesses. This included $350,000 on his own private jet company and almost $500,000 on renting his own Trump-branded properties.

One particularly interesting detail came in the form of several payments made in April to a company called "Draper Sterling" for online ads. This appears to be some mysterious entity whose name is an homage to the show Mad Men. The address listed in the filings for Draper Sterling is located in Londonderry, New Hampshire — about 20 minutes away from Lewandowski's house.

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