FBI special counsel Robert Mueller is looking into Donald Trump’s business dealings in Russia and how they aligned with his decision to run for president — and he’s using the “pee tape” dossier as a guide, according to a report from CNN.

Mueller’s team is asking questions which echo claims made in the controversial document put together by ex-British spy Christopher Steele, and focus on the possibility that Kremlin operatives possessed “kompromat” about the U.S. president which could make him subject to blackmail, according to three sources speaking to CNN.

The 35-page dossier — which was paid for by the Hillary Clinton’s campaign — claims the Russians have a kinky sex tape of the then-businessman which was recorded in the presidential suite of the Ritz Carlton hotel in Moscow where Trump visited in 2013 for the Miss Universe pageant.

Investigators are seeking detailed information about Trump’s itinerary in Moscow during his trip, specifically about the hotel room he stayed in, who had access to it, who was in charge of security and who may have visited it — including business people or government officials.

Trump has long denied all allegations made in the dossier, and his longtime bodyguard Keith Schiller told the House intelligence committee in November that he had rejected an offer by a Russian individual to send five prostitutes to Trump's hotel room, saying “he took the offer as a joke...and Trump laughed it off.”

According to the dossier, the hotel was known to be under the control of the FSB, Russia’s intelligence agency and successor to the KGB, with hidden microphones and camera in all the main rooms.

Part of Mueller’s investigation is establishing when the president became serious about running for president and whether that was linked to any of his business dealings with Russia at the time. A source told CNN that “a witness told Mueller’s team his impression was that Trump was serious about running back in 2014.”

Earlier this month Trump said he wasn’t interested in running in 2014:

Mueller’s team are also seeking information about the financing of the pageant and who paid for what. The 2013 pageant was bankrolled by Aras and Emin Agalarov, the same Russian financiers who helped arrange the infamous 2016 Trump Tower meeting with Don Trump Jr. where he was promised dirt on Hillary Clinton.

Mueller’s team is also questioning witnesses about unsuccessful discussions to brand a Trump Tower in Moscow.

Trump has said in the past that his financial affairs are outside the remit of Mueller’s investigation suggesting this latest line of inquiry is likely to irk the president even further. Trump on Monday once again dubbed the entire investigation into possible collusion with Russia a “witch hunt.”