President Trump slammed Democrats Thursday for the amount of money spent on a dossier of incendiary allegations against him, saying it was "absolutely inconceivable."

“That dossier which is totally fake and made up is like a novel, it's a disgrace and should not have been allowed to be used and then I hear the kind of money they spent," Trump told Fox News host Laura Ingraham on "The Ingraham Angle." “I mean it's inconceivable, it's absolutely inconceivable, it's horrible," he said.

The infamous dossier of opposition research on Trump was put together by Fusion GPS, a research firm retained by lawyer Marc Elias.

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The Washington Post first reported last week that former candidate Hillary Clinton Hillary Diane Rodham ClintonWhat Senate Republicans have said about election-year Supreme Court vacancies Bipartisan praise pours in after Ginsburg's death Trump carries on with rally, unaware of Ginsburg's death MORE’s campaign and the Democratic National Committee funded the dossier.

According to a report by Reuters this week, opposition research firm Fusion GPS told Congress that it paid former MI6 officer Christopher Steele's company, Orbis Business Intelligence, $168,000 in 2016 for work on the dossier.

Trump has maintained that the dossier, released before his inauguration in January, and his alleged connections to Russia were manufactured by his opponents in a political move to subvert his presidency.

"Well we're trying to figure out," Trump said on the effort to learn of who authorized the payments to the firm, "and we'll find out, and really I think it's a disgrace that a thing like that can take place."

The interview will air at 10 p.m. ET on Fox News.