Mother Jones was allowed exclusive access to a report prepared by a former spy who says the Russian government has dirt on Trump that hangs over him.
The unnamed spy and former intelligence official was originally hired by a Republican client to prepare opposition research against Trump and that's when he discovered disturbing things, such as a possibility that Trump could be blackmailed by Russian intelligence.
Mother Jones has reviewed that report and other memos this former spy wrote. The first memo, based on the former intelligence officer's conversations with Russian sources, noted, "Russian regime has been cultivating, supporting and assisting TRUMP for at least 5 years. Aim, endorsed by PUTIN, has been to encourage splits and divisions in western alliance." It maintained that Trump "and his inner circle have accepted a regular flow of intelligence from the Kremlin, including on his Democratic and other political rivals." It claimed that Russian intelligence had "compromised" Trump during his visits to Moscow and could "blackmail him." It also reported that Russian intelligence had compiled a dossier on Hillary Clinton based on "bugged conversations she had on various visits to Russia and intercepted phone calls."
We obviously don't know the accuracy of these claims, but the spy's report was delivered to the FBI which is said to be reviewing it and other cases involving ties between Trump and Russia.
As for how exactly Trump may have been "compromised," we don't know that either but apparently the FSB has a reputation for recording secret sex tapes and even producing fake ones when the need arises. People in the intelligence community and some reporters have privately (and some publicly) speculated that Russian intelligence has video of a Trump orgy. We don't know if that's true or not, but nothing about it seems implausible to me. Trump has constantly talked about sex and sexual assault his entire life.
Trump is due in court shortly after the election for allegedly raping a young girl at a sex party. The nature of those cocaine-fueled parties, which appear to be fairly common knowledge, was detailed by a witness who spoke to The Daily Beast.
The report provided by the former spy was publicly reported on by Mother Jones just hours after Slate revealed that Trump had a private server that was communicating directly with the Russian Alfa Bank.