Hours after campaign finance reports showed Donald Trump lagging far behind Hillary Clinton in fundraising, the presumptive Republican presidential nominee sent his very first fundraising email – while, in true Trump style, promising to make it the “most successful introductory fundraising email in modern political history.”

The email from Trump promises the billionaire businessman will personally match donations dollar-for-dollar over a 48-hour period, up to $2 million.

“Let's make history again, and keep winning, by making this the most successful first fundraising email ever,” Trump writes.

The fundraising blitz comes after his Federal Election Commission filing for May showed him far behind Clinton in the money race.

The reports show donors gave just over $3 million to Trump's campaign in May, while the billionaire businessman lent his effort another $2.2 million. Clinton's campaign raised more than $26 million in May, her report shows.

The biggest difference was in cash on hand.

Trump’s campaign started June with $1.3 million in the bank. Clinton’s started with $42 million.

The figures revived questions Tuesday about how Trump is funding his campaign and about his self-proclaimed wealth. Billionaire investor Mark Cuban zinged him on Twitter, saying if Trump “were fractionally as rich as he says he is, he would write a $200mm check to propel his campaign.”

Trump downplayed the fundraising gap in an interview with Fox News, on the heels of his decision to fire campaign manager Corey Lewandowski.

"We want to keep it lean. I'm not looking to spend all this money. She's going to spend more than $1 billion,” he said.

He also announced Tuesday afternoon that he has made several new hires to join his team, including veteran political operative Jim Murphy, former HR executive Lucia Castellano, digital services expert Brad Parscale, and former Bush Administration staffer Kevin Kellems.

“I continue to build a team of great people that will ensure we win in November," Trump said in a statement announcing the hires. "I have received more votes than any Republican in the history of the party and I am confident that, along with my team, we will take our movement to the White House and Make America Great Again.”

The campaign said it also added staff to the communications division, and expects to announce more hires in the department as the campaign continues to grow leading up to the convention in July.

Trump has suggested his tensions with Republican leaders were holding his operation back. He said the Republican National Committee and its chairman, Reince Priebus, "have been terrific," but "it would be nice to have full verbal support from people in office."

On both sides, past Federal Election Commission reports show Trump and Clinton are still off pace when compared with their 2012 counterparts.

In May of 2012, Mitt Romney’s campaign reported raising $23 million and ending the month with $17 million in the bank.

President Obama’s juggernaut raised $39 million and started June with nearly $110 million.

In 2008, Arizona Sen. John McCain raised $21 million in May, and ended the month with over $31 million on hand. Obama raised $23 million in that period, and had more than $43 million on hand.

The X-factor for Trump is to what extent he dips into his own private wealth. Throughout the primaries, Trump boasted that his campaign was largely self-funded. As he pivoted to the general election, he reassessed and opened the door to raising money from donors – for his campaign as well as for the Republican Party.

Whether he raises from outside sources or pays out of pocket, those expenses must be reported to the FEC.  

Fox News’ John Roberts and The Associated Press contributed to this report.