The Donald Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE campaign sent its first "emergency" fundraising email to supporters Saturday, seeking to raise at least $100,000 by the end of the day.

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That request follows a multimillion-dollar ad blitz launched by likely general election rival Hillary Clinton Hillary Diane Rodham ClintonJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Momentum growing among Republicans for Supreme Court vote before Election Day Warning signs flash for Lindsey Graham in South Carolina MORE this week.

"Right now we're facing an emergency goal of $100,000 to help get our ads on the air," the email said. "We need your contribution by 11:59 P.M. Tonight."

"Crooked Hillary is about to invade your TV with ads attacking Mr. Trump. But we're preparing to fight back," it reads, adding the campaign plans to attack Clinton over her role in Benghazi and the FBI probe into her use of a private email server while secretary of State.

Clinton, the presumptive Democratic presidential nominee, this week launched a multimillion-dollar ad blitz in eight swing states, her first geared toward the general election.

Meanwhile, Republican leaders have worried about Trump's fundraising operation as he mounts a general election campaign against Clinton's well-oiled machine.

Several prominent GOP donors have said they would keep their wallets shut this cycle and not support the unconventional candidate.

But Trump, the presumptive GOP nominee, has recently said there's "no reason" for his campaign to raise his previously pledged $1 billion for the general election.

“There’s no reason to raise that,” he said earlier this month. "I just don't think I need nearly as much money as other people need because I get so much publicity."

During the Republican primary, Trump often bragged about his largely "self-funded" campaign, but he's shown increasing willingness to court donors as next month's Republican National Convention in Cleveland draws closer.