Special counsel John Durham and his team cannot tell jurors about how the primary source for the anti-Donald Trump dossier has had links to Russian intelligence, a U.S. judge ruled on Oct. 4. The FBI opened an investigation into Igor Danchenko, the dossier source, after a colleague of Danchenko’s tipped off authorities, saying Danchenko had said he could get the person money in exchange for classified information. The FBI investigation advanced after agents learned that Danchenko had been in touch with the Russian embassy and known Russian intelligence officers and had in the past been interested in becoming a Russian...