Hillary Clinton warned supporters Monday that her campaign is in danger of being out-fundraised by Donald Trump's organization for the first time.

"With just three days left until our biggest fundraising deadline yet, we're in danger of being out-raised by the Trump campaign for the first time in this election," the Democratic nominee wrote in an email about her Republican opponent's monthly fundraising Sunday night. "That's why we've set an ambitious goal of raising $10 million online during this final week."

Twelve hours later, her campaign manager followed up and explained just how off-pace the team's August fundraising is.

"I'll be straight with you, August isn't shaping up to be our best month in terms of fundraising," Robby Mook wrote Monday morning. He said Clinton backers have just three days to cover 46 percent of the monthly goal.

A few hours later, Trump seized on his momentum and upped the ante.

"You are our only hope of stopping Hillary Clinton's Wall Street money machine. Last month Hillary and her donors outraised us by nearly $10 million. We can't let that happen again, which is why I'm setting an end-of-month goal of $10 million that we must hit," he emailed supporters. "And I'm telling you right now that if each of us makes a contribution — of any size — we will crush this 10-million dollar goal, and drive the Clinton Money Machine into a deep panic," he stated, adding that he would reach into his own pocket to double the amount of each donation.

Mook tried underscoring his camp's urgency by noting that early voting is about to start.

"We're still lagging behind where we were in July, and the timing isn't ideal," he wrote. "The first ballots will be cast in a matter of weeks, so we need to have a comprehensive, well-staffed and well-funded ground game to make sure that they're cast for Hillary."

Mook stressed that reaching monthly targets ahead of Federal Election Commission filing deadlines is about more than appearances.

"If Trump out-raises us because his team rose to the occasion, it won't just look bad; it will mean his team is more prepared than we are — right as people begin to cast their ballots," he stated.