The Trump campaign claims it pulled in $18 million in new fundraising less than 24 hours after first debate

The Trump campaign said on Tuesday that it pulled in $18 million in new fundraising, less than 24 hours after the first general-election debate between Donald Trump and his Democratic rival, Hillary Clinton.

"As a result of Donald Trump's huge debate win [Monday] night, we had a massive fundraising day, bringing in more than $18 million," campaign finance chairman, Steven Mnuchin, said in a statement Tuesday night.

Trump earlier in the day tweeted that his campaign took in $13 million. "And we're still going," he added.

Donald Trump and the GOP raised a combined $90 million in August, trailing Hillary Clinton's $143 million haul during the same month.

As recently as June, the Trump campaign had only $1.3 million in cash on hand. Trump has often boasted about running a lean operation compared to Clinton, whose campaign closed the month of June with $42.5 million.

The fundraising announcement also echoes the real-estate mogul's assertions that he won the first of what will be three general-election debates against Clinton. The match-ups are widely considered to be the most-anticipated presidential debates in modern history.

While Trump performed well in a number of online polls immediately after Monday night's event, none of those surveys were scientific, meaning those who were polled were not a representative sample of people who watched the debate.

Business Insider politics editor Oliver Darcy noted that, after the first debate, the only scientific poll was conducted by CNN/ORC, which showed viewers thought Hillary Clinton handily defeated Trump.