US President Donald Trump has seized on reports that Hillary Clinton's team bankrolled a sleazy dossier of allegations linking him to Russia.
Unfounded claims that Mr Trump had been filmed with prostitutes in a Moscow hotel surfaced in the closing stretch of last year's White House race.
Mrs Clinton's presidential campaign and the Democratic National Committee (DNC) reportedly helped fund the research.
"The victim here is the President," Mr Trump tweeted on Wednesday.
He dismissed the dossier shortly before his inauguration as "fake news".
According to US media reports, Perkins Coie, a law firm representing the Clinton campaign and DNC, hired intelligence firm Fusion GPS in April 2016.
Fusion GPS, based in Washington DC, was paid to dig up dirt on Mr Trump, who was then Mrs Clinton's rival for the presidency.
The intelligence firm subcontracted Christopher Steele, a former British spy who previously worked in Russia, to compile the research.
Attributed to unnamed sources, it claimed that Mr Trump had colluded with Russian officials during the election campaign.
The unsubstantiated dossier also alleged that Kremlin intelligence had filmed Mr Trump with prostitutes at Moscow's Ritz-Carlton hotel in 2013.
Christopher Steele, a former British spy who worked in Russia, compiled the research
The opposition research was initially funded by an unknown Republican consulting firm, which pulled the plug once Mr Trump captured the party's nomination.
The Clinton campaign then picked up the tab, according to the reports.
White House press secretary Sarah Sanders tweeted: "The real Russia scandal? Clinton campaign paid for the fake Russia dossier, then lied about it & covered it up."